Magnetic resonance imaging coated assembly

ABSTRACT

An assembly for shielding an implanted medical device from the effects of high-frequency radiation and for emitting magnetic resonance signals during magnetic resonance imaging. The assembly includes an implanted medical device and a magnetic shield comprised of nanomagnetic material disposed between the medical device and the high-frequency radiation. In one embodiment, the magnetic resonance signals are detected by a receiver, which is thus able to locate the implanted medical device within a biological organism.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation of patent application Ser. No.10/838,116 (filed May 3, 2004) which is a continuation-in-part of Ser.No. 10/384,288 (filed Mar. 7, 2003, now U.S. Pat. No. 6,765,144), whichis a continuation of co-pending application Ser. No. 10/324,773 (filedDec. 18, 2002), Ser. No. 10/313,847 (filed Dec. 7, 2002), Ser. No.10/303,264 (filed Nov. 25, 2002, now U.S. Pat. No. 6,713,671), Ser. No.10/273,738 (filed Oct. 18, 2002), Ser. No. 10/260,247 (filed Sep. 30,2002, now U.S. Pat. No. 6,673,999), Ser. No. 10/242,969 (filed Sep. 13,2002), Ser. No. 10/229,183 (filed Aug. 26, 2002), Ser. No. 10/090,553(filed Mar. 4, 2002), and Ser. No. 10/054,407 (filed Jan. 22, 2002, nowU.S. Pat. No. 6,506,972), all incorporated by reference as if fullywritten out below.

FIELD OF THE INVENTION

An assembly for imaging an implanted medical device, wherein the medicaldevice is shielded by nanomagnetic material which, in addition toshielding the medical device from high-frequency electromagneticradiation, emits high frequency electromagnetic radiation.

BACKGROUND OF THE INVENTION

Magnetic resonance imaging (“MRI”) has been developed as an imagingtechnique adapted to obtain both images of anatomical features of humanpatients as well as some aspects of the functional activities andcharacteristics of biological tissue. These images have medicaldiagnostic value in determining the state of health of the tissueexamined. Unlike the situation with fluoroscopic imaging, a patientundergoing magnetic resonance imaging procedure may remain in theactive-imaging system for a significant amount of time, e.g. a half-houror more, without suffering any adverse effects.

In an MRI process, a patient is typically aligned to place the portionof the patient's anatomy to be examined in the imaging volume of the MRIapparatus. Such an MRI apparatus typically comprises a primary magnetfor supplying a constant magnetic field (B₀) which, by convention, isalong the z-axis and is substantially homogeneous over the imagingvolume and secondary magnets that can provide linear magnetic fieldgradients along each of three principal Cartesian axes in space(generally x, y, and z, or x₁, x₂ and x₃, respectively). As is known tothose skilled in the art, a magnetic field gradient (ΔB₀/Δx_(i)) refersto the variation of the field with respect to each of the threeprincipal Cartesian axes, x_(i). The MRI apparatus also comprises one ormore RF (radio frequency) coils which provide excitation and detectionof the MRI signal. Additionally, or alternatively, detection coils maybe designed into the distal end of a catheter to be inserted into apatient. When such catheters are employed, their proximal ends areconnected to the receiving signal input channel of the magneticresonance imaging device. The detected signal is transmitted along thelength of the catheter from the receiving antenna and/or receiving coilin the distal end to the MRI input channel connected at the proximalend. Other components of an MRI system are the programmable logic unitand the various software programs which the programmable logic unitexecutes. Construction of an image from the received signals isperformed by the software of the MRI system.

The insertion of metallic wires into a biological organism (such as,e.g., catheters and guidewires) while the organism is in a magneticresonance imaging environment poses potentially deadly hazards to theorganism through excessive heating of the wires. In some studies,heating to a temperature in excess of 74 degrees Centigrade has createdsuch hazards; see, e.g., an article by M. K. Konings, et al., in“Catheters and Guidewires in Interventional MRI: Problems andSolutions”, MEDICA MUNDI 45/1 March 2001.

The Konings et al. article lists three ways in which conductors may heatup in such environments: 1) eddy currents, 2) induction loops, and 3)resonating RF transverse electromagnetic (TEM) waves along the length ofthe conductors. It is disclosed in this article that: “Because of therisks associated with metal guidewires, and catheters with metalconductors, in the MRI environment, there is an urgent need for anon-metallic substitute, both for guidewires and for signal transfer.”The authors further propose the use of “ . . . a full-glass guidewirewith a protective polymer coating . . . . ”

However, the use of such “ . . . full glass guidewire . . . ” presentsits own problems. Many medical devices (such as, e.g., guides wires,stents, etc.) require some degree of strength and flexibility that isnot afforded by glass guidewires and that typically require the use ofmetal or metal alloys in the device. The implementation of glassguidewires, optical fibers, etc., solutions would require substantialretooling of the, for example, catheter manufacturing industry and isnot a suitable solution for other medical instruments that a physicianmay wish to employ, e.g. guidewires, stents, etc, during a medicalprocedure within an MRI system.

Compositions adapted to assist in visualizing medical devices inmagnetic resonance imaging are well known. Reference may be had, e.g.,to U.S. Pat. No. 6,361,759, the entire disclosure of which is herebyincorporated by reference into this specification. This patent describesand claims: “A coating for visualizing medical devices in magneticresonance imaging, comprising a complex of formula (II): P-X-J-L-M^(n+)(II), wherein P is a polymer, X is a surface functional group selectedfrom the group consisting of an amino group and a carboxyl group, L is achelate, M is a paramagnetic ion, n is an integer that is 2 or greaterand J is the linker or spacer molecule and J is a lactam.”

U.S. Pat. No. 4,731,239 discloses and claims: “A method for nuclearmagnetic resonance (NMR) imaging of a patient comprising, prior to theNMR imaging of a patient, administering to said patient ferromagnetic,paramagnetic or diamagnetic particles effective to enhance an NMRimage.”

U.S. Pat. No. 4,989,608 discloses and claims: “A device which isspecifically useful during magnetic resonance imaging of body tissuecomprising: a flexible member of resinous material adapted to beinserted in the body tissue, the flexible member having ferromagneticparticles embedded therein at a concentration of about 0.001% to about10% by weight of the material wherein, under magnetic resonance imaging,the flexible member exhibits characteristics which differ substantiallyfrom characteristics of the body tissue so that the visibility of theflexible member under magnetic resonance imaging is substantiallyenhanced, resulting in the flexible member being distinguishable fromadjacent tissue as a dark area in brighter tissues and as a bright areain darker tissues, said member being free of elements which tend todegrade the overall quality of magnetic resonance images of the bodytissue.” At column 2 of this patent, it is disclosed that:“Ferromagnetic particles in general can cause magnetic field artifacts(MRI signal voids, with adjacent very bright signal bands, hereinaftercalled ‘imaging artifacts’ which are considerably larger than the sizeof the particle.” The entire disclosure of this patent is herebyincorporated by reference into this specification.

U.S. Pat. No. 5,154,179 discloses and claims: “1. A catheter which isspecifically useful during a magnetic resonance imaging of body tissuecomprising: a contrast agent; a flexible tubular member having a firstlumen with an additional lumen positioned therein, the additional lumenretaining the contrast agent therein; the flexible tubular member beingmade of resinous material and adapted to be inserted in the body tissue,the flexible tubular member having ferromagnetic particles embeddedtherein at a concentration of about 0.001% to about 10% by weight of thematerial wherein, under magnetic resonance imaging, the flexible memberexhibits characteristics which differ substantially from characteristicsof the body tissue so that the visibility of the flexible member undermagnetic resonance is substantially enhanced, resulting in the flexiblemember being distinguishable from adjacent tissue as a dark area inbrighter tissues and as a bright area in darker tissues, said memberbeing free of elements which tend to degrade the overall quality ofmagnetic images of the body tissue.” In the device of this patent, aferromagnetic material was extruded into plastic as the plastic wasbeing extruded to form the flexible tubular member. The entiredisclosure of this United States patent is hereby incorporated byreference in to this specification.

U.S. Pat. No. 5,462,053 discloses and claims: “1. A contrast agentadapted for magnetic resonance imaging of a sample, said contrast agentcomprising a suspension in a medium acceptable for magnetic resonanceimaging of (a) coated particles of a contrast agent possessingparamagnetic characteristics and (b) coated particles of a contrastagent possessing diamagnetic characteristics, each of said coatingsbeing selected from a group of materials which [I] renders said coatedparticles (a) and (b) substantially compatible with and substantiallybiologically and substantially chemically inert to each other and theenvironments to which said contrast agent is exposed during magneticresonance imaging and [II] which substantially stabilizes saidsuspension; the nature of each of said coatings and the relative amountsof (a) and (b) in said suspension being such that the positive magneticsusceptibility of (a) substantially offsets the negative magneticsusceptibility of (b) and the resulting suspension has substantiallyzero magnetic susceptibility and, when employed in magnetic resonanceimaging, results in the substantial elimination of imaging artifacts.”The entire disclosure of this United States patent is herebyincorporated by reference into this specification. In column 1 of thispatent, it is disclosed that: “It is well known to enhance NMR . . .images by . . . introducing into the sample to be imaged ferromagnetic,diamagnetic, or paramagnetic particles which shadow the image producedto intensity and contrast the image generated by the NMR sensitivenuclei. See, for example, the disclosures of U.S. Pat. Nos. 4,731,239;4,863,715; 4,749,560; 5,069,216; 5,055,288; 5,023,072; 4,951,674;4,827,945; and 4,770,183 . . . .”

U.S. Pat. No. 5,744,958 discloses and claims: “A magnetic resonanceimaging system, including: an imaging region and a means for generatinga magnetic resonance image of a target object in the imaging region,said magnetic resonance image including an image of the target object,wherein the means for generating the magnetic resonance image includesmeans for producing an RF field having an RF frequency in the imagingregion; and an instrument for use with the target object in the imagingregion, said instrument including: an electrically non-conductive body,sized for use with the target object in the imaging region; and anelectrically conductive, ultra-thin coating on at least part of thebody, the coating being sufficiently thick to cause the instrument to bepositively shown in the magnetic resonance image in response to presenceof the instrument in the imaging region with the target object duringgeneration of the magnetic resonance image, wherein the coating consistsof material having a skin depth with respect to said RF frequency andthe coating has a thickness less than the skin depth.” At column 4 ofthis patent, it is disclosed that: “The present invention is based onthe inventor's recognition that an electrically conductive, ‘ultra-thin’coating (a coating whose thickness is less than or of the same order ofmagnitude as the coating's skin depth with respect to its electrical andmagnetic properties and the frequency of the RF field in an MRI system)on an instrument can cause the instrument to create just enough artifactto be visible when imaged by an MRI system, but not so much artifact asto obscure or distort unacceptably the magnetic resonance imaging of atarget (e.g., human tissue) also being imaged by the MRI system. Inother words, the invention controls the artifact in such a way as tomake the instrument visible but not appreciably distort the tissuestructures being imaged by the MRI. An ultra-thin coating on aninstrument embodying the invention typically has a thickness of on theorder of hundreds or thousands of Angstroms.” The entire disclosure ofthis United States patent is hereby incorporated by reference into thisspecification.

U.S. Pat. No. 6,203,777 describes and claims: “In a method of contrastenhanced nuclear magnetic resonance diagnostic imaging which comprisesadministering into the vascular system of a subject a contrast enhancingamount of a nuclear magnetic resonance imaging contrast agent andgenerating an image of said subject, the improvement comprisingadministering as said contrast agent composite particles comprising abiotolerable, biodegradable, non-immunogenic carbohydrate orcarbohydrate derivative matrix material containing magneticallyresponsive particles, said magnetically responsive particles being of amaterial having a Curie temperature and said composite particles beingno larger than one micrometer in size.” The entire disclosure of thisUnited States patent is hereby incorporated by reference into thisspecification.

United States published patent application 2002/0176822 discloses andclaims: “A magnetic resonance imaging system, comprising: a magneticresonance device for generating a magnetic resonance image of a targetobject in an imaging region; and an instrument for use with the targetobject in the imaging region, said instrument including a body sized foruse in the target object and a polymeric-paramagnetic ion complexcoating thereon in which said complex is represented by formula (I):P—X-L-M^(n+) (I) wherein P is a polymer, X is a surface functionalgroup, L is a chelate, M is a paramagnetic ion and n is an integer thatis 2 or greater.” The entire disclosure of this United States patentapplication is hereby incorporated by reference into this specification.

None of the prior art compositions or coatings appear to be adapted toboth facilitate MRI imaging while simultaneously protecting biologicaltissue within a living organism from the adverse effects of the MRIelectromagnetic wave. By way of illustration, some of the adverseeffects include heating of tissue in contact with an implanted,conductive medical device, and voltages induced across tissue near orcontiguous with leads of implanted medical devices.

It is an object of this invention to provide an assembly for protectingbiological tissue from the adverse effects of heating during MRIscanning while simultaneously facilitating MRI imaging.

SUMMARY OF THE INVENTION

In accordance with this invention, there is provided an assembly forshielding an implanted medical device from the effects of high-frequencyradiation and for emitting magnetic resonance signals during magneticresonance imaging. The assembly includes an implanted medical device anda magnetic shield comprised of nanomagnetic material disposed betweenthe medical device and the high-frequency radiation. In one embodiment,the magnetic resonance signals are detected by a remote receiver, whichis thus able to locate the implanted medical device within a biologicalorganism.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully understood by reference to thefollowing detailed thereof, when read in conjunction with the attacheddrawings, wherein like reference numerals refer to like elements, andwherein:

FIG. 1 is a schematic sectional view of a shielded implanted devicecomprised of one preferred conductor assembly of the invention;

FIG. 1A is a flow diagram of a preferred process of the invention;

FIG. 2 is an enlarged sectional view of a portion of the conductorassembly of FIG. 1;

FIG. 3 is a sectional view of another conductor assembly of thisinvention;

FIG. 4 is a schematic view of the conductor assembly of FIG. 2;

FIG. 5 is a sectional view of the conductor assembly of FIG. 2;

FIG. 6 is a schematic of another preferred shielded conductor assembly;

FIG. 7 is a schematic of yet another configuration of a shieldedconductor assembly;

FIGS. 8A, 8B, 8C, and 8D are schematic sectional views of a substrate,such as one of the specific medical devices described in thisapplication, coated with nanomagnetic particulate matter on its exteriorsurface;

FIG. 9 is a schematic sectional view of an elongated cylinder, similarto the specific medical devices described in this application, coatedwith nanomagnetic particulate (the cylinder encloses a flexible,expandable helical member, which is also coated with nanomagneticparticulate material);

FIG. 10 is a flow diagram of a preferred process of the invention;

FIG. 11 is a schematic sectional view of a substrate, similar to thespecific medical devices described in this application, coated with twodifferent populations of elongated nanomagnetic particulate material;

FIG. 12 is a schematic sectional view of an elongated cylinder, similarto the specific medical devices described in this application, coatedwith nanomagnetic particulate, wherein the cylinder includes a channelfor active circulation of a heat dissipation fluid;

FIGS. 13A, 13B, and 13C are schematic views of an implantable cathetercoated with nanomagnetic particulate material;

FIGS. 14A through 14G are schematic views of an implantable, steerablecatheter coated with nanomagnetic particulate material;

FIGS. 15A, 15B and 15C are schematic views of an implantable guidewirecoated with nanomagnetic particulate material;

FIGS. 16A and 16B are schematic views of an implantable stent coatedwith nanomagnetic particulate material;

FIG. 17 is a schematic view of a biopsy probe coated with nanomagneticparticulate material;

FIGS. 18A and 18B are schematic views of a tube of an endoscope coatedwith nanomagnetic particulate material;

FIGS. 19A and 19B are schematics of one embodiment of the magneticallyshielding assembly of this invention;

FIGS. 20A, 20B, 20C, 20D, 20E, and 20F are enlarged sectional views of aportion of a shielding assembly illustrating nonaligned and magneticallyaligned nanomagnetic liquid crystal materials in differentconfigurations;

FIG. 21 is a graph showing the relationship of the alignment of thenanomagnetic liquid crystal material of FIGS. 20A and 20B with magneticfield strength;

FIG. 22 is a graph showing the relationship of the attenuation providedby the shielding device of this invention as a function of frequency ofthe applied magnetic field;

FIG. 23 is a flow diagram of one preferred process for preparing thenanomagnetic liquid crystal compositions of this invention;

FIG. 24 is a sectional view of a multiplayer structure comprised ofdifferent nanomagnetic materials;

FIG. 25 is a sectional view of another multilayer structure comprised ofdifferent nanomagnetic materials and an electrical insulating layer.

FIGS. 26 through 31 are schematic views of multilayer structurescomprised of nanomagnetic material;

FIGS. 32-33 are schematic illustrations of means for determining theextent to which the temperature rises in a substrate when exposed to astrong magnetic field;

FIG. 34 is a graph showing the relationship of the temperaturedifferentials in a shielded conductor and a non-conductor when each ofthem are exposed to the same magnetic field;

FIGS. 35-36 are schematics of preferred magnetic shield assemblies ofthe invention;

FIG. 37 is a phase diagram of a preferred nanomagnetic material;

FIG. 38 is a schematic of the spacing between components of thenanomagnetic material of this invention;

FIG. 39 illustrates the springback properties of one coated substrate ofthe invention;

FIGS. 40, 41, and 42 are graphs illustrating the relationship of theapplied magnetic field to the measured magnetic field when the coatedsubstrate of the invention is used as a shield;

FIGS. 43-47 are graphs depicting the properties of certain films;

FIG. 48 is a schematic of a particular assembly comprised of a layer ofnanomagnetic material;

FIG. 49 is a schematic diagram of a magnetic resonance imaging (MRI)assembly;

FIG. 50 is a sectional view of a shielded medical instrument that, whenimplanted, is adapted to produce minimal image artifacts from theelectromagnetic waves produced during MRI imaging;

FIGS. 51 and 52 are schematic representations of the effects of ahigh-frequency electromagnetic wave upon a particular substrate;

FIGS. 53 through 55 are schematic illustrations of several shieldedmedical devices that may be used in the assembly of this invention; and

FIGS. 56A, 56B, and 56C are schematic illustrations of one preferredprocess of the invention.

The present invention will be described in connection with a preferredembodiment, however, it will be understood that there is no intent tolimit the invention to the embodiment described. On the contrary, theintent is to cover all alternatives, modifications, and equivalents asmay be included within the spirit and scope of the invention as definedby the appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic sectional view of one preferred device 10 that isimplanted in a living biological organism (not shown). Device 10 iscomprised of a power source 12, a first conductor 14, a second conductor16, a first insulative shield 18 disposed about power source 12, asecond insulative shield 20 disposed about a load 22, a third insulativeshield 23 disposed about a first conductor 14, and a second conductor16, and a multiplicity of nanomagentic particles 24 disposed on saidfirst insulative shield 18 said second insulative shield 20, and saidthird insulative shield 23.

In one embodiment, the device 10 is a an implantable device used tomonitor and maintain at least one physiologic function that is capableof operating in the presence of damaging electromagnetic interference;see, e.g., United States published patent application U.S. 2002/0038135,the entire disclosure of which is hereby incorporated by reference intothis specification.

In one aspect of this embodiment, the device 10 is an implantablepacemaker. These pacemakers are well known to those skilled in the art.Reference may be had, e.g., to U.S. Pat. Nos. 5,697,959; 5,697,956(implantable stimulation device having means for optimizing currentdrain); U.S. Pat. No. 5,456,692 (method for non-invasively altering thefunction of an implanted pacemaker); U.S. Pat. No. 5,431,691 (system forrecording and displaying a sequential series of pacing events), U.S.Pat. No. 5,984,005 (multi-event bin heart rate histogram for use with animplantable pacemaker); U.S. Pat. Nos. 5,176,138; 5,003,975; 6,324,427;5,788,717; 5,417,718; 5,228,438; and the like. The entire disclosure ofeach of these United States patents is hereby incorporated by referenceinto this specification.

In the embodiment depicted in FIG. 1, the power source 12 is a battery12 that is operatively connected to a controller 26. Controller 26 isoperatively connected to the load 22 and the switch 28. Depending uponthe information furnished to controller 26, it may deliver no current,direct current, and/or current pulses to the load 22.

In one embodiment, not shown, some or all of the controller 26 and/orthe wires 30 and 32 are shielded from magnetic radiation. In anotherembodiment, not shown, one or more connections between the controller 26and the switch 28 and/or the load 22 are made by wireless means such as,e.g., telemetry means.

In one embodiment, the power source 12 provides a source of alternatingcurrent. In another embodiment, the power source 12 in conjunction withthe controller 26 provides pulsed direct current.

The load 22 may, e.g., be any of the implanted devices known to thoseskilled in the art. Thus, e.g., as described hereinabove, the load 22may be a pacemaker. Thus, e.g., load 22 may be an artificial heart.Thus, e.g., load 22 may be a heart-massaging device. Thus, e.g., load 22may be a defibrillator.

The conductors 14 and 16 may comprise conductive material(s) that have aresistivity at 20 degrees Centigrade of from about 1 to about 100microohm-centimeters. Thus, e.g., the conductive material(s) may besilver, copper, aluminum, alloys thereof, mixtures thereof, etc.

In one embodiment, the conductors 14 and 16 consist essentially of suchconductive material. Thus, e.g., in one embodiment it is preferred notto use, e.g., copper wire coated with enamel.

In the first step of one embodiment of the process of this invention,and referring to FIG. 1A and step 40, the conductive wires 14 and 16(see FIG. 1) are coated with electrically insulative material. Suitableinsulative materials include nano-sized silicon dioxide, aluminum oxide,cerium oxide, yttrium-stabilized zirconia, silicon carbide, siliconnitride, aluminum nitride, and the like. In general, these nano-sizedparticles will preferably have a particle size distribution such that atleast about 90 weight percent of the particles have a maximum dimensionin the range of from about 10 to about 100 nanometers.

The coated conductors 14 and 16 may be prepared by conventional meanssuch as, e.g., the process described in U.S. Pat. No. 5,540,959, theentire disclosure of which is hereby incorporated by reference into thisspecification. This patent describes and claims a process for preparinga coated substrate, comprising the steps of: (a) creating mist particlesfrom a liquid, wherein: said liquid is selected from the groupconsisting of a solution, a slurry, and mixtures thereof, said liquid iscomprised of solvent and from 0.1 to 75 grams of solid material perliter of solvent, at least 95 volume percent of said mist particles havea maximum dimension less than 100 microns, and said mist particles arecreated from said first liquid at a rate of from 0.1 to 30 millilitersof liquid per minute; (b) contacting said mist particles with a carriergas at a pressure of from 761 to 810 millimeters of mercury; (c)thereafter contacting said mist particles with alternating current radiofrequency energy with a frequency of at least 1 megahertz and a power ofat least 3 kilowatts while heating said mist particles to a temperatureof at least about 100 degrees centigrade, thereby producing a heatedvapor; (d) depositing said heated vapor onto a substrate, therebyproducing a coated substrate; and (e) subjecting said coated substrateto a temperature of from about 450 to about 1,400 degrees centigrade forat least about 10 minutes.

By way of further illustration, one may coat conductors 14 and 16 bymeans of the processes disclosed in a text by D. Satas entitled“Coatings Technology Handbook” (Marcel Dekker, Inc., New York, N.Y.,1991). As is disclosed in such text, one may use cathodic arc plasmadeposition (see pages 229 et seq.), chemical vapor deposition (see pages257 et seq.), sol-gel coatings (see pages 655 et seq.), and the like.One may also use one or more of the processes disclosed in this book forpreparing other coated members such as, e.g., sheath 4034 (see FIGS. 35and 36).

FIG. 2 is a sectional view of the coated conductors 14/16 of the deviceof FIG. 1. Referring to FIG. 2, and in the preferred embodiment depictedtherein, it will be seen that conductors 14 and 16 are separated byinsulating material 42. In order to obtain the structure depicted inFIG. 2, one may simultaneously coat conductors 14 and 16 with theinsulating material so that such insulators both coat the conductors 14and 16 and fill in the distance between them with insulation.

Referring again to FIG. 2, the insulating material 42 that is disposedbetween conductors 14/16 may be the same as the insulating material44/46 that is disposed above conductor 14 and below conductor 16.Alternatively, and as dictated by the choice of processing steps andmaterials, the insulating material 42 may be different from theinsulating material 44 and/or the insulating material 46. Thus, step 48(see FIG. 1A) of the process describes disposing insulating materialbetween the coated conductors 14 and 16. This step may be donesimultaneously with step 40 (see FIG. 1A); and it may be donethereafter.

The insulating material 42, the insulating material 44, and theinsulating material 46 each generally has a resistivity of from about1×10⁹ to about 1×10¹³ ohm-centimeters.

Referring again to FIG. 1A, after the insulating material 42/44/46 (seeFIG. 2) has been deposited, and in one embodiment, the coated conductorassembly is preferably heat treated in step 50. This heat treatmentoften is used in conjunction with coating processes in which the heat isrequired to bond the insulative material to the conductors 14/16 (seeFIG. 2).

The heat-treatment step may be conducted after the deposition of theinsulating material 42/44/46, or it may be conducted simultaneouslytherewith. In either event, and when it is used, it is preferred to heatthe coated conductors 14/16 (see FIG. 2) to a temperature of from about200 to about 600 degrees Centigrade for from about 1 minute to about 10minutes.

Referring again to FIG. 1A, and in step 52 of the process, after thecoated conductors 14/16 (see FIG. 2) have been subjected to heattreatment step 50, they are allowed to cool to a temperature of fromabout 30 to about 100 degrees Centigrade over a period of time of fromabout 3 to about 15 minutes.

One need not invariably heat treat and/or cool. Thus, referring to FIG.1A, one may immediately coat nanomagnetic particles onto to the coatedconductors 14/16 in step 54 either after step 48 and/or after step 50and/or after step 52.

Referring again to FIG. 1A, in step 54, nanomagnetic materials arecoated onto the previously coated conductors 14 and 16. This is bestshown in FIG. 2, wherein the nanomagnetic particles are identified asparticles 24.

In general, and as is known to those skilled in the art, nanomagneticmaterial is magnetic material which has an average particle size lessthan 100 nanometers and, preferably, in the range of from about 2 to 50nanometers. Reference may be had, e.g., to U.S. Pat. No. 5,889,091(rotationally free nanomagnetic material), U.S. Pat. Nos. 5,714,136;5,667,924; and the like. The entire disclosure of each of these UnitedStates patents is hereby incorporated by reference, into thisspecification.

The nanomagnetic materials may be, e.g., nano-sized ferrites such as,e.g., the nanomagnetic ferrites disclosed in U.S. Pat. No. 5,213,851,the entire disclosure of which is hereby incorporated by reference intothis specification. This patent claims a process for coating a layer offerritic material with a thickness of from about 0.1 to about 500microns onto a substrate at a deposition rate of from about 0.01 toabout 10 microns per minute per 35 square centimeters of substratesurface, comprising the steps of: (a) providing a solution comprised ofa first compound and a second compound, wherein said first compound isan iron compound and said second compound is selected from the groupconsisting of compounds of nickel, zinc, magnesium, strontium, barium,manganese, lithium, lanthanum, yttrium, scandium, samarium, europium,terbium, dysprosium, holmium, erbium, ytterbium, lutetium, cerium,praseodymium, thulium, neodymium, gadolinium, aluminum, iridium, lead,chromium, gallium, indium, samarium, cobalt, titanium, and mixturesthereof, and wherein said solution is comprised of from about 0.01 toabout 1,000 grams of a mixture consisting essentially of said compoundsper liter of said solution; (b) subjecting said solution to ultrasonicsound waves at a frequency in excess of 20,000 hertz, and to anatmospheric pressure of at least about 600 millimeters of mercury,thereby causing said solution to form into an aerosol; (c) providing aradio frequency plasma reactor comprised of a top section, a bottomsection, and a radio-frequency coil; (d) generating a hot plasma gaswithin said radio frequency plasma reactor, thereby producing a plasmaregion; (e) providing a flame region disposed above said top section ofsaid radio frequency plasma reactor; (f) contacting said aerosol withsaid hot plasma gas within said plasma reactor while subjecting saidaerosol to an atmospheric pressure of at least about 600 millimeters ofmercury and to a radio frequency alternating current at a frequency offrom about 100 kilohertz to about 30 megahertz, thereby forming a vapor;(g) providing a substrate disposed above said flame region; and (h)contacting said vapor with said substrate, thereby forming said layer offerritic material.

By way of further illustration, one may use the techniques described inan article by M. DeMarco, X. W. Wang, et al. on “Mossbauer andmagnetization studies of nickel ferrites” published in the Journal ofApplied Physics 73(10), May 15, 1993, at pages 6287-6289.

In general, the thickness of the layer of nanomagnetic materialdeposited onto the coated conductors 14/16 is less than about 5 micronsand generally from about 0.1 to about 3 microns.

After the nanomagnetic material is coated in step 54 of FIG. 1A, thecoated assembly may be optionally heat-treated in step 56. In thisoptional step 56, it is preferred to subject the coated conductors 14/16to a temperature of from about 200 to about 600 degrees Centigrade forfrom about 1 to about 10 minutes.

In one embodiment, illustrated in FIG. 3, one or more additionalinsulating layers 43 are coated onto the assembly depicted in FIG. 2, byone or more of the processes disclosed hereinabove. This is conducted inoptional step 58 (see FIG. 1A).

FIG. 4 is a partial schematic view of the assembly 11 of FIG. 2,illustrating the current flow in such assembly. Referring to FIG. 4, itwill be seen that current flows into conductor 14 in the direction ofarrow 60, and it flows out of conductor 16 in the direction of arrow 62.The net current flow through the assembly 11 is zero; and the netLorentz force in the assembly 11 is thus zero when placed in an externalmagnetic field (not shown). Consequently, even high current flows in theassembly 11 do not cause such assembly to move.

In the embodiment depicted in FIG. 4, conductors 14 and 16 aresubstantially parallel to each other. As will be apparent, without suchparallel orientation, there may be some net current and some net Lorentzeffect.

In the embodiment depicted in FIG. 4, and in one preferred aspectthereof, the conductors 14 and 16 preferably have the same diametersand/or the same compositions and/or the same length.

Referring again to FIG. 4, the nanomagnetic particles 24 are present ina density sufficient so as to provide shielding from magnetic flux lines64. Without wishing to be bound to any particular theory, applicantbelieves that the nanomagnetic particles 24 trap and pin the magneticlines of flux 64.

In order to function optimally, the nanomagnetic particles 24 have aspecified magnetization. As is known to those skilled in the art,magnetization is the magnetic moment per unit volume of a substance.Reference may be had, e.g., to U.S. Pat. Nos. 4,169,998; 4,168,481;4,166,263; 5,260,132; 4,778,714; and the like. The entire disclosure ofeach of these United States patents is hereby incorporated by referenceinto this specification.

Referring again to FIG. 4, the layer of nanomagnetic particles 24preferably has a saturation magnetization, at 25 degrees Centigrade, offrom about 1 to about 36,000 Gauss, or higher. In one embodiment, thesaturation magnetization at room temperature of the nanomagneticparticles is from about 500 to about 10,000 Gauss. For a discussion ofthe saturation magnetization of various materials, reference may be had,e.g., to U.S. Pat. Nos. 4,705,613; 4,631,613; 5,543,070; 3,901,741(cobalt, samarium, and gadolinium alloys), and the like. The entiredisclosure of each of these United States patents is hereby incorporatedby reference into this specification. As will be apparent to thoseskilled in the art, especially upon studying the aforementioned patents,the saturation magnetization of thin films is often higher than thesaturation magnetization of bulk objects.

In one embodiment, it is preferred to utilize a thin film with athickness of less than about 2 microns and a saturation magnetization inexcess of 20,000 Gauss. The thickness of the layer of nanomagneticmaterial is measured from the bottom surface of the layer that containssuch material to the top surface of such layer that contains suchmaterial; and such bottom surface and/or such top surface may becontiguous with other layers of material (such as insulating material)that do not contain nanomagnetic particles.

Thus, e.g., one may make a thin film in accordance with the proceduredescribed at page 156 of Nature, Volume 407, Sep. 14, 2000, thatdescribes a multilayer thin film that has a saturation magnetization of24,000 Gauss.

By the appropriate selection of nanomagnetic particles, and thethickness of the films deposited, one may obtain saturationmagnetizations of as high as at least about 36,000 Gauss.

In the preferred embodiment depicted in FIG. 4, the nanomagneticparticles 24 are disposed within an insulating matrix so that any heatproduced by such particles will be slowly dispersed within such matrix.Such matrix, as indicated hereinabove, may be made from ceria, calciumoxide, silica, alumina, and the like. In general, the insulatingmaterial 42 preferably has a thermal conductivity of less than about 20(calories-centimeters/square centimeters−degree second)×10,000. See,e.g., page E-6 of the 63^(rd) Edition of the “Handbook of Chemistry andPhysics” (CRC Press, Inc., Boca Raton, Fla., 1982).

The nanomagnetic materials 24 typically comprise one or more of iron,cobalt, nickel, gadolinium, and samarium atoms. Thus, e.g., typicalnanomagnetic materials include alloys of iron and nickel (permalloy),cobalt, niobium, and zirconium (CNZ), iron, boron, and nitrogen, cobalt,iron, boron, and silica, iron, cobalt, boron, and fluoride, and thelike. These and other materials are descried in a book by J. DouglasAdam et al. entitled “Handbook of Thin Film Devices” (Academic Press,San Diego, Calif., 2000). Chapter 5 of this book beginning at page 185,describes “magnetic films for planar inductive components and devices;”and Tables 5.1 and 5.2 in this chapter describe many magnetic materials.

FIG. 5 is a sectional view of the assembly 11 of FIG. 2. The device ofFIG. 5, and of the other Figures of this application, is preferablysubstantially flexible. As used in this specification, the term flexiblerefers to an assembly that can be bent to form a circle with a radius ofless than 2 centimeters without breaking. Put another way, the bendradius of the coated assembly 11 can be less than 2 centimeters.Reference may be had, e.g., to U.S. Pat. Nos. 4,705,353; 5,946,439;5,315,365; 4,641,917; 5,913,005; and the like. The entire disclosure ofeach of these United States patents is hereby incorporated by referenceinto this specification.

In another embodiment, not shown, the shield is not flexible. Thus, inone aspect of this embodiment, the shield is a rigid, removable sheaththat can be placed over an endoscope or a biopsy probe usedinter-operatively with magnetic resonance imaging.

In another embodiment of the invention, there is provided a magneticallyshielded conductor assembly comprised of a conductor and a film ofnanomagnetic material disposed above said conductor. In this embodiment,the conductor has a resistivity at 20 degrees Centigrade of from about 1to about 2,000 microohm-centimeters and is comprised of a first surfaceexposed to electromagnetic radiation. In this embodiment, the film ofnanomagnetic material has a thickness of from about 100 nanometers toabout 10 micrometers and a mass density of at least about 1 gram percubic centimeter, wherein the film of nanomagnetic material is disposedabove at least about 50 percent of said first surface exposed toelectromagnetic radiation, and the film of nanomagnetic material has asaturation magnetization of from about 1 to about 36,000 Gauss, acoercive force of from about 0.01 to about 5,000 Oersteds, a relativemagnetic permeability of from about 1 to about 500,000, and a magneticshielding factor of at least about 0.5. In this embodiment, thenanomagnetic material has an average particle size of less than about100 nanometers.

In one preferred embodiment of this invention, a film of nanomagneticparticles is disposed above at least one surface of a conductor.Referring to FIG. 6, and in the schematic diagram depicted therein, asource of electromagnetic radiation 100 emits radiation 102 in thedirection of film 104. Film 104 is disposed above conductor 106, i.e.,it is disposed between conductor 106 and the electromagnetic radiation102.

The film 104 is adapted to reduce the magnetic field strength at point110 relative to the field strength at point 108 (which is disposed lessthan 1 centimeter above film 104) by at least about 50 percent. Thus, ifone were to measure the magnetic field strength at point 108, andthereafter measure the magnetic field strength at point 110 (which isdisposed less than 1 centimeter below film 104), the latter magneticfield strength would be no more than about 50 percent of the formermagnetic field strength. Put another way, the film 104 has a magneticshielding factor of at least about 0.5.

In one embodiment, the film 104 has a magnetic shielding factor of atleast about 0.9, i.e., the magnetic field strength at point 110 is nogreater than about 10 percent of the magnetic field strength at point108. Thus, e.g., the static magnetic field strength at point 108 can be,e.g., one Tesla, whereas the static magnetic field strength at point 110can be, e.g., 0.1 Tesla. Furthermore, the time-varying magnetic fieldstrength of 100 milliTesla would be reduced to about 10 milliTesla ofthe time-varying field.

Referring again to FIG. 6, the nanomagnetic material 103 in film 104 hasa saturation magnetization of form about 1 to about 36,000 Gauss. Thisproperty has been discussed elsewhere in this specification. In oneembodiment, the nanomagnetic material 103 has a saturation magnetizationof from about 200 to about 26,000 Gauss.

The nanomagnetic material 103 in film 104 also has a coercive force offrom about 0.01 to about 5,000 Oersteds. The term coercive force refersto the magnetic field, H, which must be applied to a magnetic materialin a symmetrical, cyclically magnetized fashion, to make the magneticinduction, B, vanish; this term often is referred to as magneticcoercive force. Reference may be had, e.g., to U.S. Pat. Nos. 4,061,824;6,257,512; 5,967,223; 4,939,610; 4,741,953; and the like. The entiredisclosure of each of these United States patents is hereby incorporatedby reference into this specification.

In one embodiment, the nanomagnetic material 103 has a coercive force offrom about 0.01 to about 3,000 Oersteds. In yet another embodiment, thenanomagnetic material 103 has a coercive force of from about 0.1 toabout 10 Oersted.

Referring again to FIG. 6, the nanomagnetic material 103 in film 104preferably has a relative magnetic permeability of from about 1 to about500,000; in one embodiment, such material 103 has a relative magneticpermeability of from about 1.5 to about 260,000. As used in thisspecification, the term relative magnetic permeability is equal to B/H,and is also equal to the slope of a section of the magnetization curveof the film. Reference may be had, e.g., to page 4-28 of E. U. Condon etal.'s “Handbook of Physics” (McGraw-Hill Book Company, Inc., New York,1958).

Reference also may be had to page 1399 of Sybil P. Parker's “McGraw-HillDictionary of Scientific and Technical Terms,” Fourth Edition (McGrawHill Book Company, New York, 1989). As is disclosed on page 1399,permeability is “ . . . a factor, characteristic of a material, that isproportional to the magnetic induction produced in a material divided bythe magnetic field strength; it is a tensor when these quantities arenot parallel . . . . ” Relative permeability is the permeability of thematerial divided by the permeability of free space.

Reference also may be had, e.g., to U.S. Pat. Nos. 6,181,232; 5,581,224;5,506,559; 4,246,586; 6,390,443; and the like. The entire disclosure ofeach of these United States patents is hereby incorporated by referenceinto this specification.

In one embodiment, the nanomagnetic material 103 in film 104 has arelative magnetic permeability of from about 1.5 to about 2,000.

Referring again to FIG. 6, the nanomagnetic material 103 in film 104preferably has a mass density of at least about 0.001 grams per cubiccentimeter; in one embodiment, such mass density is at least about 1gram per cubic centimeter. As used in this specification, the term massdensity refers to the mass of a give substance per unit volume. See,e.g., page 510 of the aforementioned “McGraw-Hill Dictionary ofScientific and Technical Terms.” In one embodiment, the film 104 has amass density of at least about 3 grams per cubic centimeter. In anotherembodiment, the nanomagnetic material 103 has a mass density of at leastabout 4 grams per cubic centimeter.

In the embodiment depicted in FIG. 6, the film 104 is disposed above 100percent of the surfaces 112, 114, 116, and 118 of the conductor 106. Inthe embodiment depicted in FIG. 2, by comparison, the nanomagnetic filmis disposed around the conductor.

Yet another embodiment is depicted in FIG. 7. In the embodiment depictedin FIG. 7, the film 104 is not disposed in front of either surface 114,or 116, or 118 of the conductor 106. Inasmuch as radiation is notdirected towards these surfaces, this is possible.

What is essential in this embodiment, however, is that the film 104 beinterposed between the radiation 102 and surface 112. It is preferredthat film 104 be disposed above at least about 50 percent of surface112. In one embodiment, film 104 is disposed above at least about 90percent of surface 112.

Many implanted medical devices have been developed to help medicalpractitioners treat a variety of medical conditions by introducing animplantable medical device, partly or completely, temporarily orpermanently, into the esophagus, trachea, colon, biliary tract, urinarytract, vascular system or other location within a human or veterinarypatient. For example, many treatments of the vascular system entail theintroduction of a device such as a guidewire, catheter, stent,arteriovenous shunt, angioplasty balloon, a cannula or the like. Otherexamples of implantable medical devices include, e.g., endoscopes,biopsy probes, wound drains, laparoscopic equipment, urethral inserts,and implants. Most such implantable medical devices are made in whole orin part of metal, and are not part of an electrical circuit.

When a patient with one of these implanted devices is subjected to highintensity magnetic fields, such as during magnetic resonance imaging(MRI), electrical currents are induced in the metallic portions of theimplanted devices. The electrical currents so induced often createsubstantial amounts of heat. The heat can cause extensive damage to thetissue surrounding the implantable medical device.

Furthermore, when a patient with one of these implanted devicesundergoes magnetic resonance imaging (MRI), signal loss and disruptionof the diagnostic image often occur as a result of the presence of ametallic object, which causes a disruption of the local magnetic field.This disruption of the local magnetic field alters the relationshipbetween position and frequency, which are crucial for proper imagereconstruction. Therefore, patients with implantable medical devices aregenerally advised not to undergo MRI procedures. In many cases, thepresence of such a device is a strict contraindication for MRI (SeeShellock, F. G., Magnetic Resonance Procedures: Health Effects andSafety, 2001 Edition, CRC Press, Boca Raton, Fla.; also see Food andDrug Administration, Magnetic Resonance Diagnostic Device: PanelRecommendation and Report on Petitions for MR Reclassification, Federalregister, 1988, 53, 7575-7579). Any contraindication such as this,whether a strict or relative contraindication, is a serious problemsince it deprives the patient from undergoing an MRI examination, oreven using MRI to guide other therapies, such as proper placement ofdiagnostic and/or therapeutics devices including angioplasty balloons,radio frequency ablation catheters for treatment of cardiac arrythmias,sensors to assess the status of pharmacological treatment of tumors, orverification of proper placement of other permanently implanted medicaldevices. The rapidly growing capabilities and use of MRI in these andother areas prevent an increasingly large group of patients frombenefiting from this powerful diagnostic and intra-operative tool.

The use of implantable medical devices is well known in the prior art.Thus, e.g., U.S. Pat. No. 4,180,600 discloses and claims an implantablemedical device comprising a shielded conductor wire consisting of aconductive copper core and a magnetically soft alloy metallic sheathmetallurgically secured to the conductive core, wherein the sheathconsists essentially of from 2 to 5 weight percent of molybdenum, fromabout 15 to about 23 weight percent of iron, and from about 75 to about85 weight percent of nickel. Although the device of this patent doesprovide magnetic shielding, it still creates heat when it interacts withstrong magnetic fields, and it can still disrupt and distort magneticresonance images.

U.S. Pat. No. 5,817,017 discloses and claims an implantable medicaldevice having enhanced magnetic image visibility. The magnetic imagesare produced by known magnetic imaging techniques, such as MRI. Theinvention disclosed in the '017 patent is useful for modifyingconventional catheters, stents, guidewires and other implantabledevices, as well as interventional devices, such as for suturing,biopsy, which devices may be temporarily inserted into the body lumen ortissue; and it is also useful for permanently implantable devices. Theentire disclosure of this United States patent is hereby incorporated byreference into this specification.

In the process disclosed in the '017 patent, paramagnetic ionicparticles are fixedly incorporated and dispersed in selective portionsof an implantable medical device such as, e.g., a catheter. When thecatheter coated with paramagnetic ionic particles is inserted into apatient undergoing magnetic resonance imaging, the image signal producedby the catheter is of higher intensity. However, paramagnetic implants,although less susceptible to magnetization than ferromagnetic implants,can produce image artifacts in the presence of a strong magnetic field,such as that of a magnetic resonant imaging coil, due to eddy currentsgenerated in the implants by time-varying electromagnetic fields that,in turn, disrupt the local magnetic field and disrupt the image.

Any electrically conductive material, even a non-metallic material (andeven one not in an electrical circuit) will develop eddy currents andthus produce electrical potential and thermal heating in the presence ofa time-varying electromagnetic field or a radio frequency field.

Thus, there is a need to provide an implantable medical device, which isshielded from strong electromagnetic fields, which does not create largeamounts of heat in the presence of such fields, and which does notproduce image artifacts when subjected to such fields. It is one objectof the present invention to provide such a device, including a shieldingdevice that can be reversibly attached to an implantable medical device.

FIGS. 8A, 8B, 8C, and 8D are schematic sectional views of a substrate201, which is preferably a part of an implantable medical device.

Referring to FIG. 8A, it will be seen that substrate 201 is coated withnanomagnetic particles 202 on the exterior surface 203 of the substrate.

Referring to FIG. 8B, and in the embodiment depicted therein, thesubstrate 201 is coated with nanomagnetic particulate 202 on both theexterior surface 203 and the interior surface 204.

Referring to FIG. 8C, and in the preferred embodiment depicted therein,a layer of insulating material 205 separates substrate 201 and the layerof nanomagnetic coating 202.

Referring to FIG. 8D, it will be seen that one or more layers ofinsulating material 205 separate the inside and outside surfaces ofsubstrate 201 from respective layers of nanomagnetic coating 202.

FIG. 9 is a schematic sectional view of a substrate 301 which is part ofan implantable medical device (not shown). Referring to FIG. 9, and inthe embodiment depicted therein, it will be seen that substrate 301 iscoated with nanomagnetic material 302, which may differ fromnanomagnetic material 202 (see FIG. 8A).

In one embodiment, the substrate 301 is in the shape of a cylinder, suchas an enclosure for a medical catheter, stent, guidewire, and the like.In one aspect of this embodiment, the cylindrical substrate 301 enclosesa helical member 303, which is also coated with nanomagnetic particulatematerial 302.

In another embodiment (not shown), the cylindrical substrate 301depicted in FIG. 9 is coated with multiple layers of nanomagneticmaterials. In one aspect of this embodiment, the multiple layers ofnanomagnetic particulate are insulated from each other. In anotheraspect of this embodiment, each of such multiple layers is comprised ofnanomagnetic particles of different sizes and/or densities and/orchemical densities. In one aspect of this embodiment, not shown, each ofsuch multiple layers may have different thickness. In another aspect ofthis embodiment, the frequency response and degree of shielding of eachsuch layer differ from that of one or more of the other such layers.

FIG. 10 is a flow diagram of a preferred process of the invention. InFIG. 1A, reference is made to one or more conductors as being thesubstrate(s); it is to be understood, however, that other substrate(s)material(s) and/or configurations also may be used.

In the first step of this process depicted in FIG. 10, step 240, thesubstrate 201 (see FIG. 8A) is coated with electrical insulativematerial. Suitable insulative materials include nano-sized silicondioxide, aluminum oxide, cerium oxide, yttrium-stabilized zirconium,silicon carbide, silicon nitride, aluminum nitride, and the like. Ingeneral, these nano-sized particles will have a particle distributionsuch that at least 90 weight percent of the particles have a dimensionin the range of from about 10 to about 100 nanometers.

The coated substrate 201 may be prepared by conventional means such as,e.g., the process described in U.S. Pat. No. 5,540,959.

Referring again to FIGS. 8C and 8D, and by way of illustration and notlimitation, these Figures are sectional views of the coated substrate201. It will be seen that, in the embodiments depicted, insulatingmaterial 205 separates the substrate and the layer of nanomagneticmaterial 202. In order to obtain the structure depicted in FIGS. 8C and8D, one may first coat the substrate with insulating material 205, andthen apply a coat of nanomagnetic material 202 on top of the insulatingmaterial 205; see, e.g., step 248 of FIG. 10.

The insulating material 205 that is disposed between substrate 201 andthe layer of nanomagnetic coating 202 preferably has an electricalresistivity of from about 1×10⁹ to about 1×10¹³ ohm-centimeter.

After the insulating material 205 has been deposited, and in onepreferred embodiment, the coated substrate is heat-treated in step 250of FIG. 10. The heat treatment often is preferably used in conjunctionwith coating processes in which heat is required to bond the insulativematerial to the substrate 201.

The heat-treatment step 250 may be conducted after the deposition of theinsulating material 205, or it may be conducted simultaneouslytherewith. In either event, and when it is used, it is preferred to heatthe coated substrate 201 to a temperature of from about 200 to about 600degree Centigrade for about 1 minute to about 10 minutes.

Referring again to FIG. 10, and in step 252 of the process, after thecoated substrate 201 has been subjected to heat treatment step 250, thesubstrate is allowed to cool to a temperature of from about 30 to about100 degree Centigrade over a period of time of from about 3 to about 15minutes.

One need not invariably heat-treat and/or cool. Thus, referring to FIG.10, one may immediately coat nanomagnetic particulate onto the coatedsubstrate in step 254, after step 248 and/or after step 250 and/or afterstep 252.

In step 254, nanomagnetic material(s) are coated onto the previouslycoated substrate 201. This is best shown in FIGS. 8C and 8D, wherein thenanomagnetic materials are identified as 202.

In general, the thickness of the layer of nanomagnetic materialdeposited onto the coated substrate 201 is from about 100 nanometers toabout 10 micrometers and, more preferably, from about 0.1 to 3 microns.

Referring again to FIG. 10, after the nanomagnetic material is coated instep 254, the coated substrate may be heat-treated in step 256. In thisoptional step 256, it is preferred to subject the coated substrate 201to a temperature of from about 200 to about 600 degree Centigrade forfrom about 1 to about 10 minutes.

In one embodiment (not shown) additional insulating layers may be coatedonto the substrate 201, by one or more of the processes disclosedhereinabove; see, e.g., optional step 258 of FIG. 10.

Without wishing to be bound to any particular theory, the applicantsbelieve that the nanomagnetic particles 202 trap and pin magnetic linesof flux impinging on substrate 201, while at the same time minimizing oreliminating the flow of electrical currents through the coating and/orsubstrate.

Referring again to FIGS. 8A, 8B, 8C, and 8D, the layer of nanomagneticparticles 202 preferably has a saturation magnetization, at 25 degreeCentigrade, of from about 1 to about 36,000 Gauss. In one embodiment,such saturation magnetization is from about 1 to about 26,000 Gauss. Inanother embodiment, the saturation magnetization at room temperature ofthe nanomagnetic particles is from about 500 to about 10,000 Gauss.

In one embodiment, it is preferred to utilize a thin film with athickness of less than about 2 microns and a saturation magnetization inexcess of 20,000 Gauss. The thickness of the layer of nanomagneticmaterial is measured from the bottom surface of such layer that containssuch material to the top surface of such layer that contains suchmaterial; and such bottom surface and/or such top surface may becontiguous with other layers of material (such as insulating material)that do not contain nanomagnetic particles. Thus, e.g., one may make athin film in accordance with the procedure described at page 156 ofNature, Volume 407, Sep. 14, 2000, that describes a multiplayer thinfilm that has a saturation magnetization of 24,000 Gauss.

As will be apparent, even when the magnetic insulating properties of theassembly of this invention are not absolutely effective, the assemblystill reduces the amount of electromagnetic energy that is transferredto the coated substrate, prevents the rapid dissipation of heat tobodily tissue, and minimization of disruption to the magnetic resonanceimage.

FIG. 11 is a schematic sectional view of a substrate 401, which is partof an implantable medical device (not shown). Referring to FIG. 11, andin the preferred embodiment depicted therein, it will be seen thatsubstrate 401 is coated with a layer 404 of nanomagnetic material(s).The layer 404, in the embodiment depicted, is comprised of nanomagneticparticulate 405 and nanomagnetic particulate 406. Each of thenanomagnetic particulate 405 and nanomagnetic particulate 406 preferablyhas an elongated shape, with a length that is greater than its diameter.In one aspect of this embodiment, nanomagnetic particles 405 have adifferent size than nanomagnetic particles 406. In another aspect ofthis embodiment, nanomagnetic particles 405 have different magneticproperties than nanomagnetic particles 406.

Referring again to FIG. 11, and in the preferred embodiment depictedtherein, nanomagnetic particulate material 405 and nanomagneticparticulate material 406 are designed to respond to static ortime-varying electromagnetic fields or effects in a manner similar tothat of liquid crystal display (LCD) materials. More specifically, thesenanomagnetic particulate materials 405 and nanomagnetic particulatematerials 406 are designed to shift alignment and to effect switchingfrom a magnetic shielding orientation to a non-magnetic shieldingorientation. As will be apparent, the magnetic shield provided by layer404, can be turned “ON” and “OFF” upon demand. In yet another embodiment(not shown), the magnetic shield is turned on when heating of theshielded object is detected.

Reference may be had to an article by Neil Mathur et al. entitled“Mesoscopic Texture in Magnanites” (January, 2003, Physics Today) for adiscussion of the fact that “ . . . in cetain oxides of manganese, aspectacularly diverse range of exotic electronic and magnetic phases cancoexist at different locations within a single crystal. This strikingbehavior arises in manganites because their magnetic, electronic, andcrystal structures interact strongly with one another. For example, aferromagnetic metal can coexist with an insulator in which theirelectrons and their spins adopt intricate patterns.”

FIG. 12 is a schematic sectional view of substrate 501, which is part ofan implantable medical device (not shown). Referring to FIG. 12, and tothe embodiment depicted therein, it will be seen that substrate 501 iscoated with nanomagnetic particulate material 502 which may differ fromparticulate material 202 (see FIGS. 8A through 8D) and/or particulatematerial 302 (see FIG. 9) and/or materials 405 or 406 (see FIG. 11). Inthe embodiment depicted in FIG. 12, the substrate 501 may be a cylinder,such as an enclosure for a catheter, medical stent, guidewire, and thelike. The assembly depicted in FIG. 12 includes a channel 508 located onthe periphery of the medical device. An actively circulating,heat-dissipating fluid (not shown) can be pumped into channel 508through port 507, and exit channel 508 through port 509. Theheat-dissipation fluid (not shown) will draw heat to another region ofthe device, including regions located outside of the body where the heatcan be dissipated at a faster rate. In the embodiment depicted, theheat-dissipating fluid flows internally to the layer of nanomagneticparticles 502.

In another embodiment, not shown, the heat dissipating fluid flowsexternally to the layer of nanomagnetic particulate material 502.

In another embodiment (not shown), one or more additional polymer layers(not shown) are coated on top of the layer of nanomagnetic particulate502. In one aspect of this embodiment, a high thermal conductivitypolymer layer is coated immediately over the layer of nanomagneticparticulate 502; and a low thermal conductivity polymer layer is coatedover the high thermal conductivity polymer layer. It is preferred thatneither the high thermal conductivity polymer layer nor the low thermalconductivity polymer layer be electrically or magnetically conductive.In the event of the occurrence of “hot spots” on the surface of themedical device, heat from the localized “hot spots” will be conductedalong the entire length of the device before moving radially outwardthrough the insulating outer layer. Thus, heat is distributed moreuniformly.

Many different devices advantageously incorporate the nanomagnetic filmof this invention. In the following section of the specification,various additional devices that incorporate such film are described.

The disclosure in the following section of the specification relatesgenerally to an implantable medical device that is immune or hardened toelectromagnetic insult or interference. More particularly, the inventionis directed to implantable medical devices that utilize shielding toharden or make these devices immune from electromagnetic insult (i.e.minimize or eliminate the amount of electromagnetic energy transferredto the device), namely magnetic resonance imaging (MRI) insult.

Magnetic resonance imaging (MRI) has been developed as an imagingtechnique to obtain images of anatomical features of human patients aswell as some aspects of the functional activities of biological tissue;reference may be had, e.g., to John D. Enderle's “Introduction toBiomedical Engineering”, Academic Press, San Diego, Calif., 2000 and, inparticular, pages 783-841 thereof. Reference may also be had to JosephD. Bronzino's “The Biomedical Engineering Handbook”, CRC Press, BocaRaton, Fla., 1995, and in particular pages 1006-1045 thereof. Theseimages have medical diagnostic value in determining the state of thehealth of the tissue examined.

In an MRI process, a patient is typically aligned to place the portionof the patient's anatomy to be examined in the imaging volume of the MRIapparatus. Such a MRI apparatus typically comprises a primary magnet forsupplying a constant magnetic field, B₀, which is typically of fromabout 0.5 to about 10.0 Tesla, and by convention, is along the z-axisand is substantially homogenous over the imaging volume, and secondarymagnets that can provide magnetic field gradients along each of thethree principal Cartesian axis in space (generally x, y, and z or x₁,x₂, and X₃, respectively). A magnetic field gradient refers to thevariation of the field along the direction parallel to B₀ with respectto each of the three principal Cartesian Axis. The apparatus alsocomprises one or more radio frequency (RF) coils, which provideexcitation for and detection of the MRI signal. The RF excitation signalis an electromagnetic wave with an electrical field E and magnetic fieldB₁, and is typically transmitted at frequencies of 3-100 megahertz.

The use of the MRI process with patients who have implanted medicalassist devices, such as guidewires, catheters, or stents, often presentsproblems. These implantable devices are sensitive to a variety of formsof electromagnetic interference (EMI), because the aforementioneddevices contain metallic parts that can receive energy from the veryintensive EMI fields used in magnetic resonance imaging. Theabove-mentioned devices may also contain sensing and logic and controlsystems that respond to low-level electrical signals emanating from themonitored tissue region of the patient. Since these implanted devicesare responsive to changes in local electromagnetic fields, the implanteddevices are vulnerable to sources of electromagnetic noise. Theimplanted devices interact with the time-varying radio-frequency (RF)magnetic field (B₁), which are emitted during the MRI procedure. Thisinteraction can result in damage to the implantable device, or it canresult in heating of the device, which in turn can harm the patient orphysician using the device. This interaction can also result indegradation of the quality of the image obtained by the MRI process.

Signal loss and disruption of a magnetic resonance image can be causedby disruption of the local magnetic field, which perturbs therelationship between position and image, which are crucial for properimage reconstruction. More specifically, the spatial encoding of the MRIsignal provided by the linear magnetic field can be disrupted, makingimage reconstruction difficult or impossible. The relative amount ofartifact seen on an MR image due to signal disruption is dependent uponsuch factors as the magnetic susceptibility of the materials used in theimplantable medical device, as well as the shape, orientation, andposition of the medical device within the body of the patient, which isvery often difficult to control.

All non-permanently magnetized materials have non-zero magneticsusceptibilities and are to some extent magnetic. Materials withpositive magnetic susceptibilities less than approximately 0.01 arereferred to as paramagnetic and are not overly responsive to an appliedmagnetic field. They are often considered non-magnetic. Materials withmagnetic susceptibilities greater than 0.01 are referred to asferromagnetic. These materials can respond very strongly to an appliedmagnetic field and are also referred as soft magnets as their propertiesdo not manifest until exposed to an external magnetic field.

Paramagnetic materials (e.g. titanium), are frequently used toencapsulate and shield and protect implantable medical devices due totheir low magnetic susceptibilities. These enclosures operate bydeflecting electromagnetic fields. However, although paramagneticmaterials are less susceptible to magnetization than ferromagneticmaterials, they can also produce image artifacts due to eddy currentsgenerated in the implanted medical device by externally applied magneticfields, such as the radio frequency fields used in the MRI procedures.These eddy currents produce localized magnetic fields, which disrupt anddistort the magnetic resonance image. Furthermore, the implanted medicaldevice shape, orientation, and position within the body make itdifficult to control image distortion due to eddy currents induced bythe RF fields during MRI procedures. Also, since the paramagneticmaterials are electrically conductive, the eddy currents produced inthem can result in ohmic heating and injury to the patient. The voltagesinduced in the paramagnetic materials can also damage the medicaldevice, by adversely interacting with the operation of the device.Typical adverse effects can include improper stimulation of internaltissues and organs, damage to the medical device (melting of implantablecatheters while in the MRI coil have been reported in the literature),and/or injury to the patient.

Thus, it is desirable to provide protection against electromagneticinterference, and to also provide fail-safe protection against radiationproduced by magnetic-resonance imaging procedures. Moreover, it isdesirable to provide devices that prevent the possible damage that canbe done at the tissue interface due to induced electrical signals anddue to thermal tissue damage. Furthermore, it is desirable to providedevices that do not interact with RF fields which are emitted duringmagnetic-resonance imaging procedures and which result in degradation ofthe quality of the images obtained during the MRI process.

In one embodiment, there is provided a coating of nanomagnetic particlesthat consists of a mixture of aluminum oxide, iron, and other particlesthat have the ability to deflect electromagnetic fields while remainingelectrically non-conductive. Preferably the particle size in such acoating is approximately 10 nanometers. Preferably the particle packingdensity is relatively low so as to minimize electrical conductivity.Such a coating when placed on a fully or partially metallic object (suchas a guidewire, catheter, stent, and the like) is capable of deflectingelectromagnetic fields, thereby protecting sensitive internalcomponents, while also preventing the formation of eddy currents in themetallic object or coating. The absence of eddy currents in a metallicmedical device provides several advantages, to wit: (1) reduction orelimination of heating, (2) reduction or elimination of electricalvoltages which can damage the device and/or inappropriately stimulateinternal tissues and organs, and (3) reduction or elimination ofdisruption and distortion of a magnetic-resonance image.

FIGS. 13A, 13B, and 13C are schematic views of a catheter assemblysimilar to the assembly depicted in FIG. 2 of U.S. Pat. No. 3,995,623;the entire disclosure of such patent is hereby incorporated by referenceinto this specification. Referring to FIG. 6 of such patent, and also toFIGS. 13A, 13B, and 13C, it will be seen that catheter tube 625 containsmultiple lumens 603, 611, 613, and 615, which can be used for variousfunctions such as inflating balloons, enabling electrical conductors tocommunicate with the distal end of the catheter, etc. While four suchlumens are shown, it is to be understood that this invention applies toa catheter with any number of lumens.

The similar catheter disclosed and claimed in U.S. Pat. No. 3,995,623may be shielded by coating it in whole or in part with a coating ofnanomagnetic particulate.

In the embodiment depicted in FIG. 13A, interior nanomagnetic material650 a is applied to the interior wall of catheter 625, or exteriornanomagnetic material 650 b is applied to the exterior wall of catheter625, or imbibed nanomagnetic material 650 c my be imbibed into the wallsof catheter 625, or any combination of these locations.

In the embodiment depicted in FIG. 13B, internal nanomagnetic material650 d is applied to the interior walls of multiple lumens603/611/613/615 within a single catheter 625. Additionally, nonomagneticmaterials 650 b and 650 c are located on the external wall of catheter625 or imbibed into the common wall.

In the embodiment depicted in FIG. 13C, a nanomagnetic material 650 e isapplied to the mesh-like material 636 used within the wall of catheter625 to give it desired mechanical properties.

In another embodiment (not shown) a sheath coated with nanomagneticmaterial on its internal surface, exterior surface, or imbibed into thewall of such sheath, is placed over a catheter to shield it fromelectromagnetic interference. In this manner, existing catheters can bemade MRI safe and compatible. The modified catheter assembly thusproduced is resistant to electromagnetic radiation.

FIGS. 14A through 14G are schematic views of a catheter assembly 700consisting of multiple concentric elements. While two elements areshown; 720 and 722, it is to be understood that any number ofoverlapping elements may be used, either concentrically or planarlypositioned with respect to each other.

Referring to FIGS. 14A through 14G, and in the preferred embodimentdepicted therein, it will be seen that catheter assembly 700 comprisesan elongated tubular construction having a single, central or axiallumen 710. The exterior catheter body 722 and concentrically positionedinternal catheter body 720 with internal lumen 712 are preferablyflexible, i.e., bendable, but substantially non-compressible along itslength. The catheter bodies 720 and 722 may be made of any suitablematerial. A presently preferred construction comprises an outer wall 722and inner wall 720 made of a polyurethane, silicone, or nylon. The outerwall 722 preferably comprises an imbedded braided mesh of stainlesssteel or the like to increase torsional stiffness of the catheterassembly 700 so that, when a control handle, not shown, is rotated, thetip sectionally of the catheter will rotate in corresponding manner. Thecatheter assembly 700 may be shielded by coating it in whole or in partwith a coating of nanomagnetic particulate, in any one or more of thefollowing manners:

Referring to FIG. 14A, a nanomagnetic material 650 f may be coated onthe outside surface of the inner concentrically positioned catheter body720.

Referring to FIG. 14B, a nanomagnetic material 650 g may be coated onthe inside surface 713 of the inner concentrically positioned catheterbody 720.

Referring to FIG. 14C, a nanomagnetic material 650 h may be imbibed intothe walls of the inner concentrically positioned catheter body 720 andexternally positioned catheter body 722. Although not shown, ananomagnetic material may be imbibed solely into either innerconcentrically positioned catheter body 720 or externally positionedcatheter body 722.

Referring to FIG. 14D, a nancmagnetic material 650 f may be coated ontothe exterior wall of the inner concentrically positioned catheter body720 and external wall 715 (see element 650 i). Referring to FIG. 14E, ananomagnetic material 650 g may be coated onto the interior wall 713 ofthe inner concentrically positioned catheter body 720 and the externalwall 715 of externally positioned catheter body 722.

Referring to FIG. 14F, a nanomagnetic material 650 i may be coated onthe outside surface 715 of the externally positioned catheter body 722.

Referring to FIG. 14G, a nanomagnetic material 650 j may be coated ontothe exterior surface of an internally positioned solid element 727.

By way of further illustration, one may apply nanomagnetic particulatematerial to one or more of the catheter assemblies disclosed and claimedin U.S. Pat. Nos. 5,178,803; 5,041,083; 6,283,959; 6,270,477; 6,258,080;6,248,092; 6,238,408; 6,208,881; 6,190,379; 6,171,295; 6,117,064;6,019,736; 6,017,338; 5,964,757; 5,853,394; and 6,235,024; the entiredisclosure of which is hereby incorporated by reference into thisspecification. The catheters assemblies disclosed and claimed in theabove-mentioned United States patents may be shielded by coating them inwhole or in part with a coating of nanomagmetic particulate. Themodified catheter assemblies thus produced are resistant toelectromagnetic radiation.

FIGS. 15A, 15B, and 15C are schematic views of a guidewire assembly 800for insertion into vascular vessel (not shown), and it is similar to theassembly depicted in U.S. Pat. No. 5,460,187; the entire disclosure ofsuch patent is incorporated by reference into this specification.Referring to FIG. 15A, a coiled guidewire 810 is formed of a proximalsection (not shown) and central support wire 820 which terminates inhemispherical shaped tip 815. The proximal end has a retaining device(not shown) enables the person operating the guidewire to turn andorient the guidewire within the vascular conduit.

The guidewire assembly may be shielded by coating it in whole or in partwith a coating of nanomagnetic particulate.

In the embodiment depicted in FIG. 15A; the nanomagnetic material 650 iscoated on the exterior surface of the coiled guidewire 810. In theembodiment depicted in FIG. 15B; the nanomagnetic material 650 is coatedon the exterior surface of the central support wire 820. In theembodiment depicted in FIG. 15C; the nanomagnetic material 650 is coatedon all guidewire assembly components including coiled guidewire 810, tip815, and central support wire 820. The modified guidewire assembly thusproduced is resistant to electromagnetic radiation.

By way of further illustration, one may coat with nanomagneticparticulate matter the guidewire assemblies disclosed and claimed inU.S. Pat. Nos. 5,211,183; 6,168,604; 6,093,157; 6,019,737; 6,001,068;5,938,623; 5,797,857; 5,588,443; and 5,452,726; the entire disclosure ofwhich is hereby incorporated by reference into this specification. Themodified guidewire assemblies thus produced are resistant toelectromagnetic radiation.

FIGS. 16A and 16B are schematic views of a medical stent assembly 900similar to the assembly depicted in FIG. 15 of U.S. Pat. No. 5,443,496;the entire disclosure of such patent is hereby incorporated by referenceinto this specification.

Referring to FIG. 16A, a self-expanding stent 900 comprising joinedmetal stent elements 962 is shown. The stent 960 also comprises aflexible film 964. The flexible film 964 can be applied as a sheath tothe metal stent elements 962 after which the stent 900 can becompressed, attached to a catheter, and delivered through a body lumento a desired location. Once in the desired location, the stent 900 canbe released from the catheter and expanded into contact with the bodylumen, where it can conform to the curvature of the body lumen. Theflexible film 964 is able to form folds, which allow the stent elementsto readily adapt to the curvature of the body lumen. The medical stentassembly disclosed and claimed in U.S. Pat. No. 5,443,496 may beshielded by coating it in whole or in part with a nanomagnetic coating.

In the embodiment depicted in FIG. 16A, flexible film 964 is coated witha nanomagnetic coating on its inside or outside surfaces, or within thefilm itself.

In one embodiment, a stent (not shown) is coated with a nanomagneticmaterial.

It is to be understood that any one of the above embodiments may be usedindependently or in conjunction with one another within a single device.

In yet another embodiment (not shown), a sheath (not shown), coated orimbibed with a nanomagnetic material is placed over the stent,particularly the flexible film 964, to shield it from electromagneticinterference. In this manner, existing stents can be made MRI safe andcompatible.

By way of further illustration, one may coat one or more of the medicalstent assemblies disclosed and claimed in U.S. Pat. Nos. 6,315,794;6,190,404; 5,968,091; 4,969,458; 6,342,068; 6,312,460; 6,309,412; and6,305,436; the entire disclosure of each of which is hereby incorporatedby reference into this specification. The medical stent assembliesdisclosed and claimed in the above-mentioned United States patents maybe shielded by coating them in whole or in part with a coating ofnanomagmetic particulate, as described above. The modified medical stentassemblies thus produced are resistant to electromagnetic radiation.

FIG. 17 is a schematic view of a biopsy probe assembly 1000 similar tothe assembly depicted in FIG. 1 of U.S. Pat. No. 5,005,585; the entiredisclosure of such patent is hereby incorporated by reference into thisspecification. Such biopsy probe assembly 1000 is composed of threeseparate components, a hollow tubular cannula or needle 1001, a solidintraluminar rod-like stylus 1002, and a clearing rod or probe (notshown).

The components of the assembly 1000 are preferably formed of an alloy,such as stainless steel, which is corrosion resistant and non-toxic.Cannula 1001 has a proximal end (not shown) and a distal end 1005 thatis cut at an acute angle with respect to the longitudinal axis of thecannula and provides an annular cutting edge.

By way of further illustration, biopsy probe assemblies are disclosedand claimed in U.S. Pat. Nos. 4,671,292; 5,437,283; 5,494,039;5,398,690; and 5,335,663; the entire disclosure of each of which ishereby incorporated by reference into this specification. The biopsyprobe assemblies disclosed and claimed in the above-mentioned UnitedStates patents may be shielded by coating them in whole or in part witha coating of nanomagmetic particulate. Thus, e.g., cannula 1001 may becoated, intraluminar stylus 1002 may be coated, and/or the clearing rodmay be coated.

In one variation on this design (not shown), a biocompatible sheath isplaced over the coated cannula 1001 to protect the nanomagnetic coatingfrom abrasion and from contacting body fluids.

In another embodiment, the biocompatible sheath has on its interiorsurface or within its walls a nanomagnetic coating.

In yet another embodiment (not shown), a sheath coated or imbibed with ananomagnetic material is placed over the biopsy probe, to shield it fromelectromagnetic interference. The modified biopsy probe assemblies thusproduced are resistant to electromagnetic radiation.

FIGS. 18A and 18B are schematic views of a flexible tube endoscopesheath assembly 1100 similar to the assembly depicted in FIG. 1 of U.S.Pat. No. 5,058,567; the entire disclosure of such patent is herebyincorporated by reference into this specification.

MRI is increasingly being used interoperatively to guide the placementof medical devices such as endoscopes which are very good at treating orexamining tissues close up, but generally cannot accurately determinewhere the tissues being examined are located within the body.

Referring to FIG. 18A, the endoscope 1100 employs a flexible tube 1110with a distally positioned objective lens 1120. Flexible tube 1110 ispreferably formed in such manner that the outer side of a spiral tube isclosely covered with a braided-wire tube (not shown) formed by weavingfine metal wires into a braid. The spiral tube is formed using aprecipitation hardening alloy material, for example, beryllium bronze(copper-beryllium alloy).

By way of further illustration, other endoscope tube assemblies aredisclosed and claimed in U.S. Pat. Nos. 4,868,015; 4,646,723; 3,739,770;4,327,711; and 3,946,727; the entire disclosure of each of which ishereby incorporated by reference into this specification. The endoscopetube assemblies disclosed and claimed in the above-mentioned UnitedStates patents may be shielded by coating them in whole or in part witha coating of nanomagmetic particulate, material as described elsewherein this specification.

Referring again to FIG. 18A; sheath 1180 is a sheath coated withnanomagnetic material 650 a/650 b/650 c on its inside surface, itsexterior surface, or imbibed into its structure; and such sheath 1180 isplaced over the endoscope 1100, particularly the flexible tube 1110, toshield it from electromagnetic interference.

In yet another embodiment (not shown), flexible tube 1110 is coated withnanomagnetic materials on its internal surface, or imbibed withnanomagnetic materials within its wall.

In another embodiment (not shown), the braided-wire element withinflexible tube 1110 is coated with a nanomagnetic material.

In this manner, existing endoscopes can be made MRI safe and compatible.The modified endoscope tube assemblies thus produced are resistant toelectromagnetic radiation.

FIGS. 19A and 19B are schematic illustrations of a sheath assembly 2000comprised of a sheath 2002 whose surface 2004 is comprised of amultiplicity of nanomagnetic materials 2006, 2008, and 2010. In oneembodiment, the nanomagnetic material consists of or comprisesnanomagnetic liquid crystal material. Additionally, nanomagneticmaterials 2006, 2008, and 2010 may be placed on the inside surface ofsheath 2002, imbibed into the wall of sheath 2002, or any combination ofthese locations.

The sheath 2002 may be formed from electrically conductive materialsthat include metals, carbon composites, carbon nanotubes, metal-coatedcarbon filaments (wherein the metal may be either a ferromagneticmaterial such as nickel, cobalt, or magnetic or non-magnetic stainlesssteel; a paramagnetic material such as titanium, aluminum, magnesium,copper, silver, gold, tin, or zinc; a diamagnetic material such asbismuth, or well known superconductor materials), metal-coated ceramicfilaments (wherein the metal may be one of the following metals: nickel,cobalt, magnetic or non-magnetic stainless steel, titanium, aluminum,magnesium, copper, silver, gold, tin, zinc, bismuth, or well knownsuperconductor materials, a composite of metal-coated carbon filamentsand a polymer (wherein the polymer may be one of the following:polyether sulfone, silicone, polyimide, polyamide, polyvinylidenefluoride, epoxy, or urethane), a composite of metal-coated ceramicfilaments and a polymer (wherein the polymer may be one of thefollowing: polyether sulfone, silicone, polyimide, polyamide,polyvinylidene fluoride, epoxy, or urethane), a composite ofmetal-coated carbon filaments and a ceramic (wherein the ceramic may beone of the following: cement, silicates, phosphates, silicon carbide,silicon nitride, aluminum nitride, or titanium diboride), a composite ofmetal-coated ceramic filaments and a ceramic (wherein the ceramic may beone of the following: cement, silicates, phosphates, silicon carbide,silicon nitride, aluminum nitride, or titanium diboride), or a compositeof metal-coated (carbon or ceramic) filaments (wherein the metal may beone of the following metals: nickel, cobalt, magnetic or non-magneticstainless steel, titanium, aluminum, magnesium, copper, silver, gold,tin, zinc, bismuth, or well known superconductor materials), and apolymer/ceramic combination (wherein the polymer may be one of thefollowing: polyether sulfone, silicone, polymide, polyvinylidenefluoride, or epoxy and the ceramic may be one of the following: cement,silicates, phosphates, silicon carbide, silicon nitride, aluminumnitride, or titanium diboride).

In one preferred embodiment, the sheath 2002 is comprised of at leastabout 50 volume percent of the nanomagnetic material described elsewherein this specification.

As is known to those skilled in the art, liquid crystals arenonisotropic materials (that are neither crystalline nor liquid)composed of long molecules that, when aligned, are parallel to eachother in long clusters. These materials have properties intermediatethose of crystalline solids and liquids. See, e.g., page 479 of GeorgeS. Brady et al.'s “Materials Handbook,” Thirteenth Edition (McGraw-Hill,Inc., New York, 1991).

Ferromagnetic liquid crystals are known to those in the art, and theyare often referred to as FMLC. Reference may be had, e.g., to U.S. Pat.Nos. 4,241,521; 6,451,207; 5,161,030; 6,375,330; 6,130,220; and thelike. The entire disclosure of each of these United States patents ishereby incorporated by reference into this specification.

Reference also may be had to U.S. Pat. No. 5,825,448, which describes areflective liquid crystalline diffractive light valve. The figures ofthis patent illustrate how the orientations of the magnetic liquidcrystal particles align in response to an applied magnetic field. Theentire disclosure of this United States patent is hereby incorporated byreference into this specification.

Referring again to FIG. 19A, and in the embodiment depicted therein, itwill be seen that sheath 2002 may be disposed in whole or in part overmedical device 2012. In the embodiment depicted, the sheath 2002 isshown as being bigger than the medical device 2012. It will be apparentthat such sheath 2002 may be smaller than the medical device 2012, maybe the same size as the medical device 2012, may have a differentcross-sectional shape than the medical 2012, and the like.

In one preferred embodiment, the sheath 2002 is disposed over themedical device 2012 and caused to adhere closely thereto. One may createthis adhesion either by use of adhesive(s) and/or by mechanicalshrinkage.

In one embodiment, shrinkage of the sheath 2012 is caused by heat,utilizing well known shrink tube technology. Reference may be had, e.g.,to U.S. Pat. Nos. 6,438,229; 6,245,053; 6,082,760; 6,055,714; 5,903,693;and the like. The entire disclosure of each of these United Statespatents is hereby incorporated by reference into this specification.

In another embodiment of the invention, the sheath 2002 is a rigid orflexible tube formed from polytetrafluoroethylene that is heat shrunkinto resilient engagement with the implantable medical device. Thesheath can also be formed from heat shrinkable polymer materials e.g.,low density polyethylene (LDPE), linear low-density polyethylene(LLDPE), ethylene vinyl acrylate (EVA), ethylene methacrylate (EMA),ethylene methacrylate acid (EMAA) and ethyl glycol methacrylic acid(EGMA). The polymer material of the heat shrinkable sheath should have aVicat softening point less than 50 degrees Centigrade and a melt indexless than 25. A particularly suitable polymer material for the sheath ofthe invention is a copolymer of ethylene and methyl acrylate which isavailable under the trademark Lotryl 24MA005 from Elf Atochem. Thiscopolymer contains 25% methyl acrylate, has a Vicat softening point ofabout 43 degree centigrade and a melt index of about 0.5.

In another embodiment of the invention, the sheath 2002 is a collapsibletube that can be extended over the implantable medical device such as byunrolling or stretching.

In yet another embodiment of the invention, the sheath 2002 contains atearable seam along its axial length, to enable the sheath to bewithdrawn and removed from the implantable device without explanting thedevice or disconnecting the device from any attachments to its proximalend, thereby enabling the electromagnetic shield to be removed after thedevice is implanted in a patient. This is a preferable feature of thesheath, since it eliminates the need to disconnect any devices connectedto the proximal (external) end of the device, which could interrupt thefunction of the implanted medical device. This feature is particularlycritical if the shield is being applied to a life-sustaining device,such as a temporary implantable cardiac pacemaker.

The ability of the sheath 1180 (see FIGS. 18A/18B) or 2002 (see FIGS.19A/19B) to be easily removed, and therefore easily disposed, withoutdisposing of the typically much more expensive medical device beingshielded, is a preferred feature since it prevents cross-contaminationbetween patients using the same medical device.

In still another embodiment of the invention, an actively circulating,heat-dissipating fluid can be pumped into one or more internal channelswithin the sheath. The heat-dissipation fluid will draw heat to anotherregion of the device, including regions located outside of the bodywhere the heat can be dissipated at a faster rate. The heat-dissipatingflow may flow internally to the layer of nanomagnetic particles, orexternal to the layer of nanomagnetic particulate material.

FIG. 19B illustrates a process 2001 in which heat 2030 is applied to ashrink tube assembly 2003 to produce the final product 2005. For thesake of simplicity of representation, the controller 2007 has beenomitted from FIG. 19B.

Referring again to FIG. 19A, and in the preferred embodiment depictedtherein, it will be seen that a controller 2007 is connected by switch2009 to the sheath 2002. A multiplicity of sensors 2014 and 2016, e.g.,can detect the effectiveness of sheath 2002 by measuring, e.g., thetemperature and/or the electromagnetic field strength within the shield2002. One or more other sensors 2018 are adapted to measure theproperties of sheath 2002 at its exterior surface 2004.

For the particular sheath embodiment utilizing a liquid crystalnanomagnetic particle construction, and depending upon the data receivedby controller 2007, the controller 2007 may change the shieldingproperties of shield 2002 by delivering electrical and/or magneticenergy to locations 2030, 2022, 2024, etc. The choice of the energy tobe delivered, and its intensity, and its location, and its duration,will vary depending upon the status of the sheath 2002.

In the embodiment depicted in FIG. 19, the medical device may be movedin the direction of arrow 2026, while the sheath 2002 may be moved inthe direction of arrow 2028, to produce the assembly 2001 depicted inFIG. 19B. Thereafter, heat may be applied to this assembly to producethe assembly 2005 depicted in FIG. 19B.

In one embodiment, not shown, the sheath 2002 is comprised of anelongated element consisting of a proximal end and a distal end,containing one or more internal hollow lumens, whereby the lumens atsaid distal end may be open or closed, is used to temporarily orpermanently encase an implantable medical device.

In this embodiment, the elongated hollow element is similar to thesheath disclosed and claimed in U.S. Pat. No. 5,964,730; the entiredisclosure of which is hereby incorporated by reference into thisspecification.

Referring again to FIG. 19A, and in the embodiment depicted therein, thesheath 2002 is preferably coated and/or impregnated with nanomagneticshielding material 2006/2008/2010 that comprises at least 50 percent ofits external surface, and/or comprises at least 50 percent of one ormore lumen internal surfaces, or imbibed within the wall 2015 of sheath2002, thereby protecting at least fifty percent of the surface area ofone or more of its lumens, or any combination of these surfaces orareas, thus forming a shield against electromagnetic interference forthe encased medical device.

FIG. 20A is a schematic of a multiplicity of liquid crystals 2034, 2036,2038, 2040, and 2042 disposed within a matrix 2032. As will be apparent,each of these liquid crystals is comprised of nanomagnetic material2006. In the configuration illustrated in FIG. 20A, the liquid crystals2034 et seq. are not aligned.

By comparison, in the configuration depicted in FIG. 20B, such liquidcrystals 2034 are aligned. Such alignment is caused by the applicationof an external energy field (not shown).

The liquid crystals disposed within the matrix 2032 (see FIGS. 20Athrough 20F) may have different concentrations and/or compositions ofnanomagnetic particles 2006, 2009, and/or 2010; see FIG. 20C and liquidcrystals 2044, 2046, 2048, 2050, and 2052. Alternatively, oradditionally, the liquid crystals may have different shapes; see FIGS.20D, 20E, and 20F and liquid crystals 2054 and 2056, 2058, 2060, 2062,2064, and 2066. As will be apparent, by varying the size, shape, number,location, and/or composition of such liquid crystals, one may customdesign any desired response.

FIG. 21 is a graph of the response of a typical matrix 2032 comprised ofnanomagnetic liquid crystals. Three different curves, curves 2068, 2070,and 2072, are depicted, and they correspond to the responses of threedifferent nanomagnetic liquid crystal materials have different shapesand/or sizes and/or compositions.

Referring to FIG. 21, and for each of curves 2068 through 2072, it willbe seen that there is often a threshold point 2074 below which nomeaningful response to the applied magnetic field is seen; see, e.g.,the response for curve 2070.

It should be noted, however, that some materials have a low thresholdbefore they start to exhibit response to the applied magnetic field;see, e.g., curve 2068. On the other hand, some materials have a verylarge threshold; see, e.g., threshold 2076 for curve 2072.

One may produce any desired response curve by the proper combination ofnanomagnetic material composition, concentration, and location as wellas liquid crystal geometries, materials, and sizes. Other such variableswill be apparent to those skilled in the art.

Referring again to FIG. 21, it will be seen that there often is amonotonic region 2078 in which the increase of alignment of thenanomagnetic material is monotonic and often directly proportional; see,e.g., curve 2070.

There also is often a saturation point 2080 beyond which an increase inthe applied magnetic field does not substantially increase thealignment.

As will be seen from the curves in FIG. 21, the process often isreversible. One may go from a higher level of alignment to a lower levelby reducing the magnetic field applied.

The frequency of the magnetic field applied also influences the degreeof alignment. As is illustrated in FIG. 22, for one nanomagnetic liquidcrystal material (curve 2082), the response is at a maximum at aninitial frequency 2086 but then decreases to a minimum at frequency2088. By comparison, for another such curve (curve 2084), the responseis minimum at frequency 2086, increases to a maximum at point 2090, andthen decreases to a minimum at point 2092.

Thus, one may influence the response of a particular nanomagnetic liquidcrystal material by varying its type of nanomagnetic material, and/orits concentration, and/or its shape, and/or the frequency to which it issubjected. Referring again to FIG. 19A, one may affect the shieldingeffectiveness of shield 2002 by supplying a secondary magnetic field(from controller 2007) at the secondary frequencies which will elicitthe desired shielding effect.

FIG. 23 is a flow diagram illustrating a preferred process 2094 formaking nanomagnetic liquid crystal material.

Referring to FIG. 23, and in step 2100, the nanomagnetic material ofthis invention is charged to a mixer 2102 via line 2104. Thereafter,suspending medium is also charged to the mixer 2102 via line 2106.

The suspending medium may be any medium in which the nanomagneticmaterial is dispersible. Thus, e.g., the suspending medium may be a gel,it may be an aqueous solution, it may be an organic solvent, and thelike. In one embodiment, the nanomagnetic material is not soluble in thesuspending medium; in this embodiment, a slurry is produced. For thesake of simplicity of description, the use of a polymer will bedescribed in the rest of the process.

Referring again to FIG. 23, the slurry from mixer 2102 is charged vialine 2108 to mixer 2110. Thereafter, or simultaneously, polymericprecursor of liquid crystal material is also charged to mixer 2102 vialine 2104.

As is known to those skilled in the art, aromatic polyesters (liquidcrystals) may be used as such polymeric precursor. These aromaticpolyesters are commercially available as, e.g., Vectra (sold by HoechstCelanese Engineering Plastic), Xydur (sold by Amoco PerformancePlastics), Granlar (sold by Granmont), and the like. Reference may behad, e.g., to pages 649-650 of the aforementioned “Materials Handbook.”Reference also may be had, e.g., to U.S. Pat. Nos. 4,738,880; 5,142,017;5,006,402; 4,935,833; and the like. The entire disclosure of each ofthese United States patents is hereby incorporated by reference intothis specification.

Referring again to FIG. 23, the liquid crystal polymer is mixed with thenanomagnetic particles for a time sufficient to produce a substantiallyhomogeneous mixture. Typically, mixing occurs from about 5 to about 60minutes.

The polymeric material formed in mixer 2110 then is formed into adesired shape in former 2113. Thus, and referring to Joel Frados'“Plastics Engineering Handbook,” Fourth Edition (Van Nostrand ReinholdCompany, New York, N.Y., 1976), one may form the desired shape byinjection molding, extrusion, compression and transfer molding, coldmolding, blow molding, rotational molding, casting, machining, joining,and the like. Other such forming procedures are well known to thoseskilled in the art.

One may prepare several different nanomagnetic structures and join themtogether to form a composite structure. One such composite structure isillustrated in FIG. 24.

Referring to FIG. 24, assembly 2120 is comprised of nanomagneticparticles 2006, 2010, and 2008 disposed in layers 2122, 2124, and 2126,respectively. In the embodiment depicted, the layers 2122, 2124, and2126 are contiguous with each, thereby forming a continuous assembly ofnanomagnetic material, with different concentrations and compositionsthereof at different points. The response of assembly 2120 to anyparticular magnetic field will vary depending upon the location at whichsuch response is measured.

FIG. 25 illustrates an assembly 2130 that is similar to assembly 2120but that contains an insulating layer 2132 disposed between nanomagneticlayers 2134 and 2136. The insulating layer 2132 may be eitherelectrically insulative and/or thermally insulative.

FIG. 26 illustrates an assembly 2140 in which the response ofnanomagnetic material 2142 to an applied field 2143 is sensed by sensor2144 that, in the embodiment depicted, is a pickup coil 2144. Data fromsensor 2144 is transmitted to controller 2146. When and as appropriate,controller 2146 may introduce electrical and/or magnetic energy intoshielding material 2142 in order to modify its response.

FIG. 27 is a schematic illustration of an assembly 2150. In theembodiment depicted, concentric insulating layers 2152 and 2154preferably have substantially different thermal conductivities. Layer2152 preferably has a thermal conductivity that is in the range of fromabout 10 to about 2000 calories per hour per square centimeter percentimeter per degree Celsius. Layer 2154 has a thermal conductivitythat is in the range of from about 0.2 to about 10 calories per hour persquare centimeter per centimeter per degree Celsius. Layers 2152 and2154 are designed by choice of thermal conductivity and of layerthickness such that heat is conducted axially along, andcircumferentially around, layer 2152 at a rate that is between 10 timesand 1000 times higher than in layer 2154. Thus, in this embodiment, anyheat that is generated at any particular site or sites in one or morenanomagnetic shielding layers will be distributed axially along theshielded element, and circumferentially around it, before beingconducted radially to adjoining tissues. This will serve to furtherprotect these adjoining tissues from thermogenic damage even if thereare minor local flaws in the nanomagnetic shield.

Thus, in one embodiment of the invention, there is described amagnetically shielded conductor assembly, that contains a conductor, atleast one layer of nanomagnetic material, a first thermally insulatinglayer, and a second thermally insulating layer. The first thermalinsulating layer resides radially inward from said second thermallyinsulating layer, and it has a thermal conductivity from about 10 toabout 2000 calories-centimeter per hour per square centimeter per degreeCelsius. The second thermal insulating layer has a thermal conductivityfrom about 0.2 to about 10 calories per hour per square centimeter perdegree Celsius, and the axial and circumferential heat conductance ofthe first thermal insulating layer is at least about 10 to about 1000times higher than it is for said second thermal insulating layer.

In another embodiment of the invention, there is provided a magneticallyshielded conductor assembly as discussed hereinabove, in which the firstthermally insulating layer is disposed between said conductor and saidlayer of nanomagnetic material, and the second thermally insulatinglayer is disposed outside said layer of nanomagnetic material

In another embodiment, there is provided a magnetically shieldedconductor assembly as discussed hereinabove wherein the first thermallyinsulating layer is disposed outside the layer of nanomagnetic material,and wherein the second thermally insulating layer is disposed outsidesaid first layer of thermally insulating material.

In another embodiment, the shield is comprised of a abrasion-resistantcoating comprised of nanomagnetic material. Referring to FIG. 28, itwill be seen that shield 2170 is comprised of abrasion resistant coating2172 and nanomagnetic layer 2174.

A Composite Shield

In this portion of the specification, applicants will describe oneembodiment of a composite shield of their invention. This embodimentinvolves a shielded assembly comprised of a substrate and, disposedabove a substrate, a shield comprising from about 1 to about 99 weightpercent of a first nanomagnetic material, and from about 99 to about 1weight percent of a second material with a resistivity of from about 1microohm-centimeter to about 1×10²⁵ microohm centimeters.

FIG. 29 is a schematic of a preferred shielded assembly 3000 that iscomprised of a substrate 3002. The substrate 3002 may be any one of thesubstrates illustrated hereinabove. Alternatively, or additionally, itmay be any receiving surface which it is desired to shield from magneticand/or electrical fields. Thus, e.g., the substrate can be substantiallyany size, any shape, any material, or any combination of materials. Theshielding material(s) disposed on and/or in such substrate may bedisposed on and/or in some or all of such substrate.

By way of illustration and not limitation, the substrate 3002 may be,e.g., a foil comprised of metallic material and/or polymeric material.The substrate 3002 may, e.g., comprise ceramic material, glass material,composites, etc. The substrate 3002 may be in the shape of a cylinder, asphere, a wire, a rectilinear shaped device (such as a box), anirregularly shaped device, etc.

In one embodiment, the substrate 3002 preferably has a thickness of fromabout 100 nanometers to about 2 centimeters. In one aspect of thisembodiment, the substrate 3002 preferably is flexible.

Referring again to FIG. 29, and in the preferred embodiment depictedtherein, it will be seen that a shield 3004 is disposed above thesubstrate 3002. As used herein, the term “above” refers to a shield thatis disposed between a source 3006 of electromagnetic radiation 102 andthe substrate 3002. The shield 3004 may be contiguous with the substrate3002, or it may not be contiguous with the substrate 3002.

The shield 3004, in the embodiment depicted, is comprised of from about1 to about 99 weight percent of nanomagnetic material 3008; suchnanomagnetic material, and its properties, are described elsewhere inthis specification. In one embodiment, the shield 3004 is comprised ofat least about 40 weight percent of such nanomagnetic material 3008. Inanother embodiment, the shield 3004 is comprised of at least about 50weight percent of such nanomagnetic material 3008.

Referring again to FIG. 29, and in the preferred embodiment depictedtherein, it will be seen that the shield 3004 is also comprised ofanother material 3010 that preferably has an electrical resistivity offrom about 1 microohm-centimeter to about 1×10²⁵ microohm-centimeters.This material 3010 is preferably present in the shield at aconcentration of from about 1 to about 99 weight percent and, morepreferably, from about 40 to about 60 weight percent.

In one embodiment, the material 3010 has a dielectric constant of fromabout 1 to about 50 and, more preferably, from about 1.1 to about 10. Inanother embodiment, the material 3010 has resistivity of from about 3 toabout 20 microohm-centimeters.

In one embodiment, the material 3010 preferably is a nanoelectricalmaterial with a particle size of from about 5 nanometers to about 100nanometers.

In another embodiment, the material 3010 has an elongated shape with anaspect ratio (its length divided by its width) of at least about 10. Inone aspect of this embodiment, the material 3010 is comprised of amultiplicity of aligned filaments.

In one embodiment, the material 3010 is comprised of one or more of thecompositions of U.S. Pat. Nos. 5,827,997 and 5,643,670. The entiredisclosure of each of these United States patents is hereby incorporatedby reference into this specification.

Thus, e.g., the material 3010 may comprise filaments, wherein eachfilament comprises a metal and an essentially coaxial core, eachfilament having a diameter less than about 6 microns, each corecomprising essentially carbon, such that the incorporation of 7 percentvolume of this material in a matrix that is incapable of electromagneticinterference shielding results in a composite that is substantiallyequal to copper in electromagnetic interference shielding effectives at1-2 gigahertz. Reference may be had, e.g., to U.S. Pat. No. 5,827,997.

In another embodiment, the material 3010 is a particulate carbon complexcomprising: a carbon black substrate, and a plurality of carbonfilaments each having a first end attached to said carbon blacksubstrate and a second end distal from said carbon black substrate,wherein said particulate carbon complex transfers electrical current ata density of 7000 to 8000 milliamperes per square centimeter for aFe⁺²/Fe⁺³ oxidation/reduction electrochemical reaction couple carriedout in an aqueous electrolyte solution containing 6 millmoles ofpotassium ferrocyanide and one mole of aqueous potassium nitrate.

In another embodiment, the material 3010 is a diamond-like carbonmaterial. As is known to those skilled in the art, this diamond-likecarbon material has a Mohs hardness of from about 2 to about 15 and,preferably, from about 5 to about 15. Reference may be had, e.g., toU.S. Pat. No. 5,098,737 (amorphic diamond material); U.S. Pat. No.5,658,470 (diamond-like carbon for ion milling magnetic material); U.S.Pat. No. 5,731,045 (application of diamond-like carbon coatings totungsten carbide components); U.S. Pat. No. 6,037,016 (capacitativelycoupled radio frequency diamond-like carbon reactor); U.S. Pat. No.6,087,025 (application of diamond like material to cutting surfaces),and the like. The entire disclosure of each of these United Statespatents is hereby incorporated by reference into this specification.

In another embodiment, material 3010 is a carbon nanotube material.These carbon nanotubes generally have a cylindrical shape with adiameter of from about 2 nanometers to about 100 nanometers, and lengthof from about 1 micron to about 100 microns.

These carbon nanotubes are well known to those skilled in the art.Reference may be had, e.g., to U.S. Pat. No. 6,203,864 (heterojunctioncomprised of a carbon nanotube), U.S. Pat. No. 6,361,861 (carbonnanotubes on a substrate), U.S. Pat. No. 6,445,006 (microelectronicdevice comprising carbon nanotube components), U.S. Pat. No. 6,457,350(carbon nanotube probe tip), and the like. The entire disclosure of eachof these United States patents is hereby incorporated by reference intothis specification.

In one embodiment, material 3010 is silicon dioxide particulate matterwith a particle size of from about 10 nanometers to about 100nanometers.

In another embodiment, the material 3010 is particulate alumina, with aparticle size of from about 10 to about 100 nanometers. Alternatively,or additionally, one may use aluminum nitride particles, cerium oxideparticles, yttrium oxide particles, combinations thereof, and the like;regardless of the particle(s) used in this embodiment, it is preferredthat its particle size be from about 10 to about 100 nanometers.

In the embodiment depicted in FIG. 29, the shield 3004 is preferably inthe form of a layer of material that has a thickness of from about 100nanometers to about 10 microns. In this embodiment, both thenanomagnetic particles 3008 and the electrical particles 3010 arepresent in the same layer.

In the embodiment depicted in FIG. 30, by comparison, the shield 3012 iscomprised of layers 3014 and 3016. The layer 3014 is comprised of atleast about 50 weight percent of nanomagnetic material 3008 and,preferably, at least about 90 weight percent of such nanomagneticmaterial 3008. The layer 3016 is comprised of at least about 50 weightpercent of electrical material 3010 and, preferably, at least about 90weight percent of such electrical material 3010.

In the embodiment depicted in FIG. 30, the layer 3014 is disposedbetween the substrate 3002 and the layer 3016. In the embodimentdepicted in FIG. 31, the layer 3016 is disposed between the substrate3002 and the layer 3014.

Each of the layers 3014 and 3016 preferably has a thickness of fromabout 10 nanometers to about 5 microns.

In one embodiment, the shield 3012 has an electromagnetic shieldingfactor of at least about 0.5 and, more preferably, at least about 0.9.In one embodiment, the electromagnetic field strength at point 3020 isno greater than about 10 percent of the electromagnetic field strengthat point 3022.

In one preferred embodiment, illustrated in FIG. 31, the nanomagneticmaterial 3008 and/or 3010 preferably has a mass density of at leastabout 0.01 grams per cubic centimeter, a saturation magnetization offrom about 1 to about 36,000 Gauss, a coercive force of from about 0.01to about 5000 Oersteds, a relative magnetic permeability of from about 1to about 500,000, and an average particle size of less than about 100nanometers.

Determination of the Heat Shielding Effect of the Magnetic Shield

FIG. 32 is a schematic representation of a test which may be used todetermine the extent to which the temperature of a conductor 4000 israised by exposure to strong electromagnetic radiation 3006. In thistest, the radiation 3006 is representative of the fields present duringMRI procedures. As is known to those skilled in the art, such fieldstypically include a static field with a strength of from about 0.5 toabout 2 Teslas, a radio frequency alternating magnetic field with astrength of from about 20 microTeslas to about 100 microTeslas, and agradient magnetic field that has three components—x, y, and z, each ofwhich has a field strength of from about 0.05 to 500 milliTeslas.

The test depicted in FIG. 32 is conducted in accordance with A.S.T.M.Standard Test F-2182-02, “Standard test method for measurement ofradio-frequency induced heating near passive implant during magneticresonance imaging.” Referring again to FIG. 32, a temperature probe 4002is used to measure the temperature of an unshielded conductor 4000 whensubjected to the magnetic field 3006 in accordance with such A.S.T.M.F-2182-02.

The same test is then performed upon a shielded conductor assembly 4010that is comprised of the conductor 4000 and a magnetic shield 4004, asshown in FIG. 33.

The magnetic shield used may comprise nanomagnetic particles, asdescribed hereinabove. Alternatively, or additionally, it may compriseother shielding material, such as, e.g., oriented nanotubes (see, e.g.,U.S. Pat. No. 6,265,466). The entire disclosure of this United Statespatent is hereby incorporated by reference into this specification.

In the embodiment depicted in FIG. 33, the shield 4004 is in the form ofa layer of shielding material with a thickness 4006 of from about 10nanometers to about 1 millimeter. In one embodiment, the thickness 4006is from about 10 nanometers to about 20 microns.

In one preferred embodiment, illustrated in FIG. 33, the shieldedconductor 4010 is implantable device and is connected to a pacemakerassembly 4012 comprised of a power source 4014, a pulse generator 4016,and a controller 4018. The pacemaker assembly 4012 and its associatedshielded conductor 4010 are preferably disposed within a livingbiological organism 4020.

Referring again to FIG. 33, and in the preferred embodiment depictedtherein, it will be seen that shielded conductor assembly 4010 comprisesa means 4011 for transmitting signals to and from the pacemaker 4012 andthe biological organism 4020.

In one preferred embodiment, the conductor 4000 is flexible, that is, atleast a portion 4022 of the conductor 4000 is capable of being flexed atan angle 4024 of least 15 degrees by the application of a force 4026 notto exceed about 1 dyne.

Referring again to FIG. 33, when the shielded assembly is tested inaccordance with A.S.T.M. 2182-02, it will have a specified temperatureincrease, as is illustrated in FIG. 34.

As is shown in FIG. 34, the “dTs” is the change in temperature of theshielded assembly 4010 when tested in accordance with such A.S.T.M.test. The “dTc” is the change in temperature of the unshielded conductor4000 using precisely the same test conditions but omitting the shield4004. The ratio of dTs/dTc is the temperature increase ratio; and thetemperature increase ratio is defined as the heat shielding factor.

It is preferred that the shielded conductor assembly 4010 have a heatshielding factor of less than about 0.2. In one embodiment, the shieldedconductor assembly 4010 has a heat shielding factor of less than aboutleast 0.3.

FIGS. 35 and 36 are sectional views of shielded conductor assembly 4030and 4032. Each of these assemblies is comprised of a flexible conductor4000, a layer 4004 of magnetic shielding material, and a sheath 4034.

The sheath 4034 preferably is comprised of antithrombogenic material. Inone embodiment, the sheath 4034 preferably has a coefficient of frictionof less than about 0.1.

Antithrombogenic compositions and structures have been well known tothose skilled in the art for many years. As is disclosed, e.g., in U.S.Pat. No. 5,783,570, the entire disclosure of which is herebyincorporated by reference into this specification, “Artificial materialssuperior in processability, elasticity and flexibility have been widelyused as medical materials in recent years. It is expected that they willbe increasingly used in a wider area as artificial organs such asartificial kidney, artificial lung, extracorporeal circulation devicesand artificial blood vessels, as well as disposable products such assyringes, blood bags, cardiac catheters and the like. These medicalmaterials are required to have, in addition to sufficient mechanicalstrength and durability, biological safety which particularly means theabsence of blood coagulation upon contact with blood, i.e.,antithrombogenicity.”

“Conventionally employed methods for imparting antithrombogenicity tomedical materials are generally classified into three groups of (1)immobilizing a mucopolysaccharide (e.g., heparin) or a plasminogenactivator (e.g., urokinase) on the surface of a material, (2) modifyingthe surface of a material so that it carries negative charge orhydrophilicity, and (3) inactivating the surface of a material. Ofthese, the method of (1) (hereinafter to be referred to briefly assurface heparin method) is further subdivided into the methods of (A)blending of a polymer and an organic solvent-soluble heparin, (B)coating of the material surface with an organic solvent-soluble heparin,(C) ionic bonding of heparin to a cationic group in the material, and(D) covalent bonding of a material and heparin.”

“Of the above methods, the methods (2) and (3) are capable of affordinga stable antithrombogenicity during a long-term contact with bodyfluids, since protein adsorbs onto the surface of a material to form abiomembrane-like surface. At the initial stage when the material hasbeen introduced into the body (blood contact site) and when variouscoagulation factors etc. in the body have been activated, however, it isdifficult to achieve sufficient antithrombogenicity without ananticoagulant therapy such as heparin administration.”

Other antithrombogenic methods and compositions are also well known.Thus, by way of further illustration, United States published patentapplication 2001/0016611 discloses an antithrombogenic compositioncomprising an ionic complex of ammonium salts and heparin or a heparinderivative, said ammonium salts each comprising four aliphatic alkylgroups bonded thereto, wherein an ammonium salt comprising fouraliphatic alkyl groups having not less than 22 and not more than 26carbon atoms in total is contained in an amount of not less than 5% andnot more than 80% of the total ammonium salt by weight. The entiredisclosure of this published patent application is hereby incorporatedby reference into this specification.

Thus, e.g., U.S. Pat. No. 5,783,570 discloses an organic solvent-solublemucopolysaccharide consisting of an ionic complex of at least onemucopolysaccharide (preferably heparin or heparin derivative) and aquaternary phosphonium, an antibacterial antithrombogenic compositioncomprising said organic solvent-soluble mucopolysaccharide and anantibacterial agent (preferably an inorganic antibacterial agent such assilver zeolite), and to a medical material comprising said organicsolvent soluble mucopolysaccharide. The organic solvent-solublemucopolysaccharide, and the antibacterial antithrombogenic compositionand medical material containing same are said to easily impartantithrombogenicity and antibacterial property to a polymer to be a basematerial, which properties are maintained not only immediately afterpreparation of the material but also after long-term elution. The entiredisclosure of this United States patent is hereby incorporated byreference into this specification.

By way of further illustration, U.S. Pat. No. 5,049,393 disclosesanti-thrombogenic compositions, methods for their production andproducts made therefrom. The anti-thrombogenic compositions comprise apowderized anti-thrombogenic material homogeneously present in asolidifiable matrix material. The anti-thrombogenic material ispreferably carbon and more preferably graphite particles. The matrixmaterial is a silicon polymer, a urethane polymer or an acrylic polymer.The entire disclosure of this United States patent is herebyincorporated by reference into this specification.

By way of yet further illustration, U.S. Pat. No. 5,013,717 discloses aleach resistant composition that includes a quaternary ammonium complexof heparin and a silicone. A method for applying a coating of thecomposition to a surface of a medical article is also disclosed in thepatent. Medical articles having surfaces which are both lubricious andantithrombogenic, are produced in accordance with the method of thepatent. The entire disclosure of this United States patent is herebyincorporated by reference into this specification.

Referring again to FIG. 35, and in the preferred embodiment depictedtherein, the sheath 4034 is non contiguous with the layer 4004; in thisembodiment, another material 4036 (such as, e.g., air) is present. InFIG. 36, by comparison, the sheath 4034 is contiguous with the layer4004.

In both of the embodiments depicted in FIGS. 35 and 36, the conductor4000 preferably has a resistivity at 20 degrees Centigrade of from about1 to about 100 micro ohm-centimeters.

In one embodiment, not shown, the sheath 4034 is omitted and the shield4004 itself is comprised of and/or acts as an antithrombogeniccomposition. In one aspect of this embodiment, the outer surface 4037 ofsheath 4034 is hydrophobic. In another aspect of this embodiment, theouter surface 4037 of the sheath is hydrophilic. Similarly, in theembodiments depicted in FIGS. 35 and 36, the outer surface 4037 of thesheath 4034 can be either hydrophobic or hydrophilic.

In this embodiment, the conductor assembly is comprised of a magneticshield disposed above said flexible conductor, wherein said magneticshield is comprised of an antithrombogenic composition, wherein saidmagnetic shield is comprised of a layer of magnetic shielding material,and wherein said layer of magnetic shielding material, when exposed to amagnetic field with a intensity of at least about 30 microTesla, has amagnetic shielding factor of at least about 0.5. In one embodiment, theconductor assembly has a heat shielding factor of at least about 0.2

A Process for Preparation of an Iron-containing Thin Film

In one preferred embodiment of the invention, a sputtering technique isused to prepare an AlFe thin film as well as comparable thin filmscontaining other atomic moieties, such as, e.g., elemental nitrogen, andelemental oxygen. Conventional sputtering techniques may be used toprepare such films by sputtering. See, for example, R. Herrmann and G.Brauer, “D.C.—and R. F. Magnetron Sputtering,” in the “Handbook ofOptical Properties: Volume I—Thin Films for Optical Coatings,” edited byR. E. Hummel and K. H. Guenther (CRC Press, Boca Raton, Fla., 1955).Reference also may be had, e.g., to M. Allendorf, “Report of Coatings onGlass Technology Roadmap Workshop,” Jan. 18-19, 2000, Livermore, Calif.;and also to U.S. Pat. No. 6,342,134, “Method for producing piezoelectricfilms with rotating magnetron sputtering system.” The entire disclosureof each of these prior art documents is hereby incorporated by referenceinto this specification.

Although the sputtering technique is preferred, the plasma techniquedescribed elsewhere in this specification also may be used.

One may utilize conventional sputtering devices in this process. By wayof illustration and not limitation, a typical sputtering system isdescribed in U.S. Pat. No. 5,178,739, the entire disclosure of which ishereby incorporated by reference into this specification. As isdisclosed in this patent, “ . . . a sputter system 10 includes a vacuumchamber 20, which contains a circular end sputter target 12, a hollow,cylindrical, thin, cathode magnetron target 14, a RF coil 16 and a chuck18, which holds a semiconductor substrate 19. The atmosphere inside thevacuum chamber 20 is controlled through channel 22 by a pump (notshown). The vacuum chamber 20 is cylindrical and has a series ofpermanent, magnets 24 positioned around the chamber and in closeproximity therewith to create a multipole field configuration near theinterior surface 15 of target 12. Magnets 26, 28 are placed above endsputter target 12 to also create a multipole field in proximity totarget 12. A singular magnet 26 is placed above the center of target 12with a plurality of other magnets 28 disposed in a circular formationaround magnet 26. For convenience, only two magnets 24 and 28 are shown.The configuration of target 12 with magnets 26, 28 comprises a magnetronsputter source 29 known in the prior art, such as the Torus-10E systemmanufactured by K. Lesker, Inc. A sputter power supply 30 (DC or RF) isconnected by a line 32 to the sputter target 12. A RF supply 34 providespower to RF coil 16 by a line 36 and through a matching network 37.Variable impedance 38 is connected in series with the cold end 17 ofcoil 16. A second sputter power supply 39 is connected by a line 40 tocylindrical sputter target 14. A bias power supply 42 (DC or RF) isconnected by a line 44 to chuck 18 in order to provide electrical biasto substrate 19 placed thereon, in a manner well known in the priorart.”

By way of yet further illustration, other conventional sputteringsystems and processes are described in U.S. Pat. No. 5,569,506 (amodified Kurt Lesker sputtering system); U.S. Pat. No. 5,824,761 (aLesker Torus 10 sputter cathode); U.S. Pat. Nos. 5,768,123; 5,645,910;6,046,398 (sputter deposition with a Kurt J. Lesker Co. Torus 2 sputtergun); U.S. Pat. Nos. 5,736,488; 5,567,673; 6,454,910; and the like. Theentire disclosure of each of these United States patents is herebyincorporated by reference into this specification.

By way of yet further illustration, one may use the techniques describedin a paper by Xingwu Wang et al. entitled “Technique Devised forSputtering AlN Thin Films,” published in “the Glass Researcher,” Volume11, No. 2 (Dec. 12, 2002). The entire disclosure of this publication ishereby incorporated by reference into this specification.

In one preferred embodiment, a magnetron sputtering technique isutilized, with a Lesker Super System III system. The vacuum chamber ofthis system is cylindrical, with a diameter of approximately one meterand a height of approximately 0.6 meters. The base pressure used is fromabout 0.001 to 0.0001 Pascals. In one aspect of this process, the targetis a metallic FeAl disk, with a diameter of approximately 0.1 meter. Themolar ratio between iron and aluminum used in this aspect isapproximately 70/30. Thus, the starting composition in this aspect isalmost non-magnetic. See, e.g., page 83 (FIG. 3.1aii) of R. S. Tebble etal.'s “Magnetic Materials” (Wiley-Interscience, New York, N.Y., 1969);this Figure discloses that a bulk composition containing iron andaluminum with at least 30 mole percent of aluminum (by total moles ofiron and aluminum) is substantially non-magnetic.

In this aspect, to fabricate FeAl films, a DC power source is utilized,with a power level of from about 150 to about 550 watts (Advanced EnergyCompany of Colorado, model MDX Magnetron Drive). The sputtering gas usedin this aspect is argon, with a flow rate of from about 0.0012 to about0.0018 standard cubic meters per second. To fabricate FeAlN films inthis aspect, in addition to the DC source, a pulse-forming device isutilized, with a frequency of from about 50 to about 250 MHz (AdvancedEnergy Company, model Sparc-Ie V). One may fabricate FeAlO films in asimilar manner but using oxygen rather than nitrogen.

In this aspect, a typical argon flow rate is from about (0.9 to about1.5)×10⁻³ standard cubic meters per second; a typical nitrogen flow rateis from about (0.9 to about 1.8)×10⁻³ standard cubic meters per second;and a typical oxygen flow rate is from about. (0.5 to about 2)×10⁻³standard cubic meters per second. During fabrication, the pressuretypically is maintained at from about 0.2 to about 0.4 Pascals. Such apressure range is found to be suitable for nanomagnetic materialsfabrications.

In this aspect, the substrate used may be either flat or curved. Atypical flat substrate is a silicon wafer with or without a thermallygrown silicon dioxide layer, and its diameter is preferably from about0.1 to about 0.15 meters. A typical curved substrate is an aluminum rodor a stainless steel wire, with a length of from about 0.10 to about0.56 meters and a diameter of from (about 0.8 to about 3.0)×10⁻³ metersThe distance between the substrate and the target is preferably fromabout 0.05 to about 0.26 meters.

In this aspect, in order to deposit a film on a wafer, the wafer isfixed on a substrate holder. The substrate may or may not be rotatedduring deposition. In one embodiment, to deposit a film on a rod orwire, the rod or wire is rotated at a rotational speed of from about0.01 to about 0.1 revolutions per second, and it is moved slowly backand forth along its symmetrical axis with a maximum speed of about 0.01meters per second.

In this aspect, to achieve a film deposition rate on the flat wafer of5×10⁻¹⁰ meters per second, the power required for the FeAl film is 200watts, and the power required for the FeAlN film is 500 watts. Theresistivity of the FeAlN film is approximately one order of magnitudelarger than that of the metallic FeAl film. Similarly, the resistivityof the FeAlO film is about one order of magnitude larger than that ofthe metallic FeAl film.

Iron containing magnetic materials, such as FeAl, FeAlN and FeAlO, havebeen fabricated by various techniques. The magnetic properties of thosematerials vary with stoichiometric ratios, particle sizes, andfabrication conditions; see, e.g., R. S. Tebble and D. J. Craik,“Magnetic Materials”, pp. 81-88, Wiley-Interscience, New York, 1969. Asis disclosed in this reference, when the iron molar ratio in bulk FeAlmaterials is less than 70 percent or so, the materials will no longerexhibit magnetic properties.

However, it has been discovered that, in contrast to bulk materials, athin film material often exhibits different properties due to theconstraint provided by the substrate.

Nanomagnetic Compositions Comprised of Moieties A, B, and C

The aforementioned process described in the preceding section of thisspecification may be adapted to produce other, comparable thin films, asis illustrated in FIG. 37.

Referring to FIG. 37, and in the preferred embodiment depicted therein,a phase diagram 5000 is presented. As is illustrated by this phasediagram 5000, the nanomagnetic material used in the composition of thisinvention preferably is comprised of one or more of moieties A, B, andC.

The moiety A depicted in phase diagram 5000 is comprised of a magneticelement selected from the group consisting of a transition series metal,a rare earth series metal, or actinide metal, a mixture thereof, and/oran alloy thereof.

As is known to those skilled in the art, the transition series metalsinclude chromium, manganese, iron, cobalt, nickel. One may use alloys oriron, cobalt and nickel such as, e.g., iron-aluminum, iron-carbon,iron-chromium, iron-cobalt, iron-nickel, iron nitride (Fe₃N), ironphosphide, iron-silicon, iron-vanadium, nickel-cobalt, nickel-copper,and the like. One may use alloys of manganese such as, e.g.,manganese-aluminum, manganese-bismuth, MnAs, MnSb, MnTe,manganese-copper, manganese-gold, manganese-nickel, manganese-sulfur andrelated compounds, manganese-antimony, manganese-tin, manganese-zinc,Heusler alloy, and the like. One may use compounds and alloys of theiron group, including oxides of the iron group, halides of the irongroup, borides of the transition elements, sulfides of the iron group,platinum and palladium with the iron group, chromium compounds, and thelike.

One may use a rare earth and/or actinide metal such as, e.g., Ce, Pr,Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, La, mixtures thereof,and alloys thereof. One may also use one or more of the actinides suchas, e.g., Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr, Ac, andthe like.

These moieties, compounds thereof, and alloys thereof are well known andare described, e.g., in the aforementioned text of R. S. Tebble et al.entitled “Magnetic Materials.”

In one preferred embodiment, moiety A is selected from the groupconsisting of iron, nickel, cobalt, alloys thereof, and mixturesthereof. In this embodiment, the moiety A is magnetic, i.e., it has arelative magnetic permeability of from about 1 to about 500,000. As isknown to those skilled in the art, relative magnetic permeability is afactor, characteristic of a material, that is proportional to themagnetic induction produced in a material divided by the magnetic fieldstrength; it is a tensor when these quantities are not parallel. See,e.g., page 4-128 of E. U. Condon et al.'s “Handbook of Physics”(McGraw-Hill Book Company, Inc., New York, N.Y., 1958).

The moiety A also preferably has a saturation magnetization of fromabout 1 to about 36,000 Gauss, and a coercive force of from about 0.01to about 5,000 Oersteds.

The moiety A may be present in the nanomagnetic material either in itselemental form, as an alloy, in a solid solution, or as a compound.

It is preferred at least about 1 mole percent of moiety A be present inthe nanomagnetic material (by total moles of A, B, and C), and it ismore preferred that at least 10 mole percent of such moiety A be presentin the nanomagnetic material (by total moles of A, B, and C). In oneembodiment, at least 60 mole percent of such moiety A is present in thenanomagnetic material, (by total moles of A, B, and C.)

In addition to moiety A, it is preferred to have moiety B be present inthe nanomagnetic material. In this embodiment, moieties A and B areadmixed with each other. The mixture may be a physical mixture, it maybe a solid solution, it may be comprised of an alloy of the A/Bmoieties, etc.

In one embodiment, the magnetic material A is dispersed withinnonmagnetic material B. This embodiment is depicted schematically inFIG. 38.

Referring to FIG. 38, and in the preferred embodiment depicted therein,it will be seen that A moieties 5002, 5004, and 5006 are separated fromeach other either at the atomic level and/or at the nanometer level. TheA moieties may be, e.g., A atoms, clusters of A atoms, A compounds, Asolid solutions, etc; regardless of the form of the A moiety, it has themagnetic properties described hereinabove.

In the embodiment depicted in FIG. 38, each A moiety produces anindependent magnetic moment. The coherence length (L) between adjacent Amoieties is, on average, from about 0.1 to about 100 nanometers and,more preferably, from about 1 to about 50 nanometers.

Thus, referring again to FIG. 38, the normalized magnetic interactionbetween adjacent A moieties 5002 and 5004, and also between 5004 and5006, is preferably described by the formula M=exp(−x/L), wherein M isthe normalized magnetic interaction, exp is the base of the naturallogarithm (and is approximately equal to 2.71828), x is the distancebetween adjacent A moieties, and L is the coherence length.

In one embodiment, and referring again to FIG. 38, x is preferablymeasured from the center 5001 of A moiety 5002 to the center 5003 of Amoiety 5004; and x is preferably equal to from about 0.00001×L to about100×L.

In one embodiment, the ratio of x/L is at least 0.5 and, preferably, atleast 1.5.

Referring again to FIG. 37, the nanomagnetic material may be comprisedof 100 percent of moiety A, provided that such moiety A has the requirednormalized magnetic interaction (M). Alternatively, the nanomagneticmaterial may be comprised of both moiety A and moiety B.

When moiety B is present in the nanomagnetic material, in whatever formor forms it is present, it is preferred that it be present at a moleratio (by total moles of A and B) of from about 1 to about 99 percentand, preferably, from about 10 to about 90 percent.

The B moiety, in whatever form it is present, is nonmagnetic, i.e., ithas a relative magnetic permeability of 1.0; without wishing to be boundto any particular theory, applicants believe that the B moiety acts asbuffer between adjacent A moieties. One may use, e.g., such elements assilicon, aluminum, boron, platinum, tantalum, palladium, yttrium,zirconium, titanium, calcium, beryllium, barium, silver, gold, indium,lead, tin, antimony, germanium, gallium, tungsten, bismuth, strontium,magnesium, zinc, and the like.

In one embodiment, and without wishing to be bound to any particulartheory, it is believed that B moiety provides plasticity to thenanomagnetic material that it would not have but for the presence of B.It is preferred that the bending radius of a substrate coated with bothA and B moieties be at least 110 percent as great as the bending radiusof a substrate coated with only the A moiety.

The use of the B material allows one to produce a coated substrate witha springback angle of less than about 45 degrees. As is known to thoseskilled in the art, all materials have a finite modulus of elasticity;thus, plastic deformations followed by some elastic recovery when theload is removed. In bending, this recovery is called springback. See,e.g., page 462 of S. Kalparjian's “Manufacturing Engineering andTechnology,” Third Edition (Addison Wesley Publishing Company, New York,N.Y., 1995).

FIG. 39 illustrates how springback is determined in accordance with thisinvention. Referring to FIG. 39, a coated substrate 5010 is subjected toa force in the direction of arrow 5012 that bends portion 5014 of thesubstrate to an angle 5016 of 45 degrees, preferably in a period of lessthan about 10 seconds. Thereafter, when the force is released, the bentportion 5014 springs back to position 5018. The springback angle 5020 ispreferably less than 45 degrees and, preferably, is less than about 10degrees.

Referring again to FIG. 38, when an electromagnetic field 5022 isincident upon the nanomagnetic material 5026 comprised of A and B (seeFIG. 38), such a field will be reflected to some degree depending uponthe ratio of moiety A and moiety B. In one embodiment, it is preferredthat at least 1 percent of such field is reflected in the direction ofarrow 5024. In another embodiment, it is preferred that at least about10 percent of such field is reflected. In yet another embodiment, atleast about 90 percent of such field is reflected. Without wishing to bebound to any particular theory, applicants believe that the degree ofreflection depends upon the concentration of A in the A/B mixture.

M, the normalized magnetic interaction, preferably ranges from about3×10⁻⁴⁴ to about 1.0. In one preferred embodiment, M is from about 0.01to 0.99. In another preferred embodiment, M is from about 0.1 to about0.9.

Referring again to FIG. 37, and in one embodiment, the nanomagneticmaterial is comprised of moiety A, moiety C, and optionally moiety B.The moiety C is preferably selected from the group consisting ofelemental oxygen, elemental nitrogen, elemental carbon, elementalfluorine, elemental chlorine, elemental hydrogen, elemental helium,elemental neon, elemental argon, elemental krypton, elemental xenon, andthe like.

It is preferred, when the C moiety is present, that it be present in aconcentration of from about 1 to about 90 mole percent, based upon thetotal number of moles of the A moiety and/or the B moiety and C moietyin the composition.

Referring again to FIG. 37, and in the embodiment depicted, the area5028 produces a composition which optimizes the degree to which magneticflux are initially trapped and/or thereafter released by the compositionwhen a magnetic field is withdrawing from the composition.

Without wishing to be bound to any particular theory, applicants believethat, when a composition as described by area 5028 is subjected to analternating magnetic field, at least a portion of the magnetic field istrapped by the composition when the field is strong, and then thisportion tends to be released when the field lessens in intensity. Thistheory is illustrated in FIG. 40.

Referring to FIG. 40, at time zero, the magnetic field 5022 applied tothe nanomagnetic material starts to increase, in a typical sine wavefashion. After a specified period of time 5030, a magnetic moment iscreated within the nanomagnetic material; but, because of the timedelay, there is a phase shift.

FIG. 41 illustrates how a portion of the magnetic field 5022 is trappedwithin the nanomagnetic material and thereafter released. Referring toFIG. 41, it will be seen that the applied field 5022 is trapped after atime delay 5030 within the nanomagnetic material and thereafter, atpoint 5032, starts to release; at point 5034, the trapped flux is almostcompletely released.

The time delay 5030 (see FIGS. 40/41) will vary with the composition ofthe nanomagnetic material. By maximizing the amount of trapping, and byminimizing the amount of reflection and absorption, one may minimize themagnetic artifacts caused by the nanomagnetic shield.

Thus, one may optimize the A/B/C composition to preferably be within thearea 5028 (see FIG. 37). In general, the A/B/C composition has molarratios such that the ratio of A/(A and C) is from about 1 to about 99mole percent and, preferably, from about 10 to about 90 mole percent. Inone preferred embodiment, such ratio is from about 40 to about 60 molarpercent.

The molar ratio of A/(A and B and C) generally is from about 1 to about99 mole percent and, preferably, from about 10 to about 90 molarpercent. In one embodiment, such molar ratio is from about 30 to about60 molar percent.

The molar ratio of B/(A plus B plus C) generally is from about 1 toabout 99 mole percent and, preferably, from about 10 to about 40 molepercent.

The molar ratio of C/(A plus B plus C) generally is from about 1 toabout 99 mole percent and, preferably, from about 10 to about 50 molepercent.

In one embodiment, the composition of the nanomagnetic material ischosen so that the applied electromagnetic field 5022 is absorbed by thenanomagnetic material by less than about 1 percent; thus, in thisembodiment, the applied magnetic field 5022 is substantially restored bycorrecting the time delay 5030. Referring to FIG. 41, and to theembodiment depicted, the applied magnetic field 5022 and the measuredmagnetic field 5023 are substantially identical, with the exception oftheir phases.

In another embodiment, illustrated in FIG. 42, the measured field 5025is substantially different from the applied field 5022. In thisembodiment, an artifact will be detected by the magnetic field measuringdevice (not shown). The presence of such an artifact, and its intensity,may be used to detect and quantify the exact location of the coatedsubstrate. In this embodiment, one preferably would use an area outsideof area 5028 (see FIG. 37), such as, e.g., area 5036.

In another embodiment, also illustrated in FIG. 42, the measured field5025 has less intensity than the applied field 5022. One may increasethe amount of absorption of the nanomagnetic material to produce ameasured field like measured field 5025 by utilizing the area 5036 ofFIG. 37.

By utilizing nanomagnetic material that absorbs the electromagneticfield, one may selectively direct energy to various cells that are to betreated. Thus, e.g., cancer cells can be injected with the nanomagneticmaterial and then destroyed by the application of externally appliedelectromagnetic fields. Because of the nano size of applicants'materials, they can readily and preferentially be directed to themalignant cells to be treated within a living organism. In thisembodiment, the nanomagnetic material preferably has a particle size offrom about 5 to about 10 nanometers and, thus, can be used in a mannersimilar to a tracer.

In one embodiment, the nanomagnetic material is injected into apatient's bloodstream. In another embodiment, the nanomagnetic materialis inhaled by a patient. In another embodiment, it is digested by apatient. In another embodiment, it is implanted through conventionalmeans. In each of these embodiments, conventional diagnostic means maybe utilized to determine when such material has reached to the targetsite(s), and then intense electromagnetic radiation may then be timelyapplied.

Example of the Preparation of a Nanomagnetic Material Coating

The following examples are presented to illustrate the preparation ofnanomagnetic material but are not to be deemed limitative thereof.Unless otherwise specified, all parts are by weight, and alltemperatures are in degrees Celsius.

In these examples, the fabrication of nanomagnetic materials wasaccomplished by a novel PVD sputtering process. A Kurt J. Lesker SuperSystem III deposition system outfitted with Lesker Torus 4 magnetronswas utilized; the devices were manufactured by the Kurt J. LekserCompany of Clairton, Pa.

The vacuum chamber of the system used in these examples was cylindrical,with a diameter of approximately one meter and a height of about 0.6meters. The base pressure used was from 1 to 2 micro-torrs.

The target used was a metallic FeAl disk with a diameter of about 0.1meters. The molar ratio between the Fe and Al atoms was about 70/30.

In order to fabricate FeAl films, a direct current power source asutilized at a power level of from 150 to 550 watts; the power source wasan Advanced Energy MDX Magnetron Drive.

The sputtering gas used was argon, with a flow rate of from 15 to 35sccm.

In order to fabricate FeAlN films, a pulse system was added in serieswith the DC power supply to provide pulsed DC. The magnetron polarityswitched from negative to positive at a frequency of 100 kilohertz, andthe pulse width for the positive or negative duration was adjusted toyield suitable sputtering results (Advanced Energy Sparc-1e V).

In addition to using argon flowing at a rate of from 15 to 25 sccm,nitrogen was supplied as a reactive gas with a flow rate of from 15 to30 sccm. During fabrication, the pressure was maintained at 2-4milli-torrs.

The substrate used was either a flat disk or a cylindrical rod. Atypical flat disk used was a silicon wafer with or without a thermallygrown silicon dioxide layer, with a diameter of from 0.1 to 0.15 meters.The thickness of the silicon dioxide layer was 50 nanometers. A typicalrod was an aluminum rod or a stainless steel wire with a length of from0.1 to 0.56 meters and a diameter of from 0.0008 to 0.003 meters.

The distance between the substrate and the target was from 0.05 to 0.26meters. To deposit a film on a wafer, the wafer was fixed on a substrateholder, and there was no rotational motion. To deposit a film on a rodof wire, the rod or wire was rotated at a speed of from 0.01 to 0.1revolutions per second and was moved slowly back and forth along itssymmetrical axis with the maximum speed being 0.01 meters per second.

A typical film thickness was between 100 nanometers and 1 micron, and atypical deposition time was between 200 and 2000 seconds. Theresistivity of an FelAl films was approximately 8×10⁻⁶ Ohm-meter. Theresistivity of an FeAlN film is approximately 200×10⁻⁶ Ohm-meter. Theresistivity of an FeAlO film was about 0.01 Ohm-meter.

The fabrication conditions used for FeAlO films was somewhat differentthan those used for FeAl films. With the former films, the target wasFeAlO, and the source was radio frequency with a power of about 900watts.

Materials Characterization

According to surface profiler and SEM cross-sectional measurements, thefilm thickness variation in a flat area of 0.13 meters×0.13 meters waswithin 10 percent. As revealed by AFM measurement, the surface roughnessof an FeAl film was about 3 nanometers, and that of an FeAlN film wasabout 2 nanometers. All films were under compressive stress with thevalues for FeAl films under 355×10⁶ Pascal, and those for FeAlN filmsunder 675×10⁶ Pascal.

In order to determine the average chemical composition of a film, EDSwas utilized to study the composition at four spots of the film, with aspot size of about 10 microns×10 microns×10 microns. For an FeAl film,the molar ratio of Fe/Al was about 39/61; and, for an FeAlN film, themolar ration of Fe/Al/N was about 19/25/56.

In each of the films, the Fe/Al ratio was different from that in thetarget; and the relative iron concentration was lower than the effectivealuminum concentration.

The surface chemistry was studied via XPS. It was found that, on the topsurface of an FeAl film, within the top 10 nanometers, oxygen waspresent in addition to Fe and Al; and the molar ratio of Fe/AI/O was17/13/70. It was found that, on the top surface of an FeAlN film oxygenwas also present in addition to Fe, Al, and N; and the molar ratio ofFe/AI/N/0 was 20/13/32/34.

In contrast to the average chemical composition of the films, on thesurface of the FeAl or FeAlN films, the relative iron concentration washigher than the relative aluminum concentration. To observe thevariations of the Fe/Al ratio below the top surface, SIMS was utilized.It was found that the relative Fe/Al ratio decreases as the distancefrom the top increases.

Both XRD and TEM were utilized to study the phase formation. FIG. 43illustrates the XRD pattern for an FeAl film. Besides broad amorphouspeaks, the major peak around 44 degrees coincides with the maindiffraction peaks of FeAl alloys, such as AlFe₃ (JCPDS Card number45-1203), and Al_(0.4)Fe_(0.6) (JCPDS Card number 45-0982). The averagecrystal size was estimated to be 7 nanometers by a computer programcalled “SHADOW” (S. A. Howard, “SHADOW: A system for X-ray powderdiffraction pattern analysis: Annotated program listings and tutorial,”University of Missouri-Rolla, 1990).

SEM analyses confirmed that both amorphous and crystalline phases werepresent in the films, and the sizes of the crystals were between 10nanometers and 30 nanometers.

The XRD pattern of an FeAlN film indicated that several broaddiffraction patterns are present, suggesting an amorphous growth. Thisamorphous growth was confirmed by TEM. For FeAlO films, as revealed byXRD and TEM, amorphous growth was the dominating mechanism.

Magnetic Properties

For an FeAl film with a thickness of about 500 nanometers, the real partof the relative permeability was about 40 in a direct current field andan alternating current field with a frequency lower than 200 Megahertz,and the imaginary part of the permeability is nearly zero at frequencieslower than 200 Megahertz. In FIG. 44, the real and imaginary parts ofthe permeability were plotted as functions of frequency between 200Megahertz and 1.8 GHz. The value of the real part increases slightly asthe frequency increases, reaching a maximum value of 100 near 1.4 GHz,and it decreases to zero near 1.7 GHz. The value of the imaginary partreaches its maximum value at 1.6 GHz. Thus, the ferromagnetic resonancefrequency of the film is near 1.6 GHz. In FIG. 45, a hysteresis loop forthe FeAl film is illustrated. The loop appeared to have two sections.One section was in the region between plus and minus 100 G, which hassome squareness similar to that illustrated in FIG. 4 for a thinnerfilm. The other section was either was 100 G and 400 G, or between −100G and −400 G, which may be indicating that the effective magnetic momentis approximately 0.046 emu, and the saturation magnetization, 4πMs, is9,120 Gauss. The effective anisotropy field is approximately 400 G. Foranother FeAl film, with a thickness of about 150 nanometers, a magneticloop measured with VSM (at 300K) is illustrated in FIG. 46. The coerciveforce (Hc) was approximately 30 Oersted, the remanence magnetic momentwas about 0.0044 emu, and the saturation magnetic moment was about0.0056 emu. Thus, the squareness of the loop was about 80 percent.Correspondingly, the remanence magnetization (4πMr) is about 2,908 G,and the saturation magnetization (4πMs) is about 3700 G. For an FeAlNfilm, with a thickness of about 414 nanometers, a magnetic hysteresisloop measured with SQUID (at 5 K) is illustrated in FIG. 47. Thecoercive force, Hc, is about 40 Oersted, the remanence magnetic momentwas about 0.000008 emu, and the saturation magnetic moment was about0.000025 emu. Correspondingly, the remanence magnetization was about 64G, and the saturation magnetization was about 2,000 G. The relativepermeability was about 3.3. At 300 K, the value of the relativepermeability is reduced to one, and the values of Hc, Mr, and Ms arealso reduced.

For FeAlO films with thicknesses between 145 and 189 nanometers, thehysteresis loop of each film is similar to the FeAlN film. At 300 K, therelative permeability ranges from 0.28 to 3.3, Hc ranges from 20 to 132Oe, 4πMr ranges from 12 to 224 G, and 4πMs ranges from 800 to 1,640 G.The ferromagnetic resonance frequency of an FeAlO film is about 9.5Gigahertz.

FIG. 48 is a schematic of a composite structure 5100 comprised of alayer 5102 material that acts as a hermetic seal and/or isbiocompatible. The layer 5102 is disposed over insulator layer 5104;insulator layer 5104, in one embodiment, is not continuous.

The insulator layer 5104 is disposed over a layer 5106 of nanomagneticmaterial; in one embodiment, nanomagnetic material layer 5106 is notcontinuous. Layer 5106 is disposed over a layer 5108 of insulativematerial that, in turn, is disposed over conductor layer 5110.

As will be apparent, the use of the insulating/dielectric layers 5104and 5104 together with the conductor layer 5110 has an effect upon thecapacitance of the structure 5100. Similarly, the use of the layer 5106of nanomagnetic material affects the inductance of the structure 5100.

By varying the characteristics and the properties of the insulatorlayers 5104/5108, and of the nanomagnetic material 5106, one can, e.g.,increase both the capacitance and the inductance of the system. In oneembodiment, the inductance of system 5100 increases substantially, butthe capacitance is not changed much.

A Novel Magnetic Resonance Imaging Assembly

In another embodiment of this invention, there is provided a magneticresonance imaging assembly which utilizes an implanted medical devicethat does not heat substantially during exposure to MRI radiation butwhich, nonetheless, provides detectable feedback from such radiation.

In one aspect of this embodiment, there is provided a magnetic resonanceimaging tracking assembly that comprises a medical device comprising amagnetic shield, means for generating a first high frequencyelectromagnetic wave, means for sensing a modified high-frequencyelectromagnetic wave, means for producing an image from said modifiedhigh-frequency electromagnetic wave, and means for modifying said imageproduced from said modified high-frequency electromagnetic wave.

FIG. 49 is a block diagram illustrating the components of a typicalmagnetic resonance imaging (MRI) unit 6000. This MRI unit 6000 iscomprised of means 6014 for producing certain types of electromagneticradiation. Such radiation is generally comprised of alternatingelectromagnetic waves with a frequency of at least about 21 megahertz,depending on B₀.

MRI units with the capability of producing such electromagneticradiation are well known. Reference may be had, e.g., to U.S. Pat. No.4,733,189 (magnetic resonance imaging systems); U.S. Pat. No. 4,449,097(nuclear magnetic resonance systems); U.S. Pat. No. 5,867,027 (magneticresonance imaging apparatus); U.S. Pat. No. 5,568,051 (magneticresonance imaging apparatus having superimposed gradient coil); U.S.Pat. No. 5,329,232 (magnetic resonance methods and apparatus); and thelike. The entire disclosure of each of these United States patents ishereby incorporated by reference into this specification.

Referring again to FIG. 49, and in the preferred embodiment depictedtherein, it will be seen that MRI unit 6000 comprises an imaging volume6012 into which a patient or other sample to be imaged is placed. Insome MRI units, only a portion of the patient is placed within theimaging volume 6012 while the rest of the patient is outside the imagingvolume 6012.

In many MRI units, the imaging volume 6012 is the space enclosed by oneor more MRI coils. The patient is disposed within such space andimpacted over a 360-degree radius by radiation from such coils.

Thus, and referring again to FIG. 49 and to the embodiment depictedtherein, the MRI system 6000 preferably contains coils 6014 that, in oneembodiment, are usually comprised of a main coil (not shown) forgenerating a uniform magnetic field (not shown) through the imagingvolume 6012. The coils 6014 also preferably comprise gradient coils (notshown) to generate linear gradient magnetic variation in the imagingvolume 6012, radio frequency transmit coils (not shown) for transmittinga magnetic resonance excitation signal train, and one or more pickupcoils (not shown) to receive the de-excitation nuclear signals from theimaging sample placed in the imaging volume 6012. Reference may be had,e.g., to U.S. Pat. No. 4,860,221 (magnetic resonance imaging system),U.S. Pat. No. 5,184,074 (real-time MR imaging inside gantry room), U.S.Pat. No. 5,874,831 (magnetic resonance imaging system), U.S. Pat. No.5,779,637 (magnetic resonance imaging system including an imageacquisition apparatus rotator), U.S. Pat. No. 5,332,972 (gradientmagnetic field generator for MRI system), and the like. The entiredisclosure of each of these United States patents is hereby incorporatedby reference into this specification.

As will be apparent to those skilled in the art, one may utilize othercoils. In one embodiment, an imaging pickup coil(s) (not shown) whichdefines the imaging volume 6012 as the volume which the pickup coil(s)(not shown) are sensitive to, is placed inside a patient. Reference maybe had, e.g., to U.S. Pat. No. 5,476,095 (intracavity probe andinterface device for MRI imaging and spectroscopy); U.S. Pat. No.5,451,232 (probe for MRI imaging and spectroscopy particularly in thecervical region); U.S. Pat. No. 5,307,814 (externally moveableintracavity probe for MRI imaging and spectroscopy); U.S. Pat. No.6,263,229 (miniature magnetic resonance catheter coils and relatedmethods); U.S. Pat. No. 6,171,240 (MRI RF Catheter Coil); and the like.The entire disclosure of each of these United States patents is herebyincorporated by reference into this specification.

Referring again to FIG. 49, and to the preferred embodiment depictedtherein, the MRI unit 6000 preferably contains one or more programmablelogic units (PLU) 6016 for controlling the coils (6014). In theembodiment depicted, the PLU processes the received signals and createsan image of an internal region (not shown) of the patient (not shown).See, e.g., the United States patents cited above as well as U.S. Pat.No. 6,445,182 (geometric distortion correction in magnetic resonanceimaging); U.S. Pat. No. 6,046,591 (MRI system with fractional decimationof acquired data); and U.S. Pat. No. 6,414,487 (time and memoryoptimized method of acquiring and reconstructing multi-shotthree-dimensional MRI data). The entire disclosure of each of theseUnited States patents is hereby incorporated by reference into thisspecification.

Referring again to FIG. 49, an image is displayed onto a display screen6020. This and other tasks of the PLU 6016 are controlled by thesoftware 6018 which the PLU executes.

In one embodiment, and referring again to FIG. 49, the software 6018 isadapted to apply different signal filtering and image filteringalgorithms to the received signals. Thus, if some characteristic of thereceived signal is known to be caused by known material in the imagingvolume 6012, it is possible to enhance or eliminate the known materialfrom the displayed image. For example, bone will have a different MRIde-excitation signal than tissue. It is therefore possible to programthe software to enhance the tissue signal and the tissue image displayedto the physician while diminishing the signal from the bone material,thus diminishing or eliminating the bone image in the final displayedimage. This may be accomplished in part by filtering the receivedsignals.

Manipulation of the image data collected by an MRI system, as well asthe manipulation of the re-constructed image, is well known to thoseskilled in the art. Reference may be had to U.S. Pat. No. 6,459,922(post data-acquisition method for generating water/fat separated MRimages having adjustable relaxation contrast). This patent discloses “Apost data-acquisition magnetic resonance imaging (MRI) method isdisclosed for generating water/fat separated MR images wherein theresultant contrast in water-only or fat-only images is made adjustableunder operator control.” The entire disclosure of this United Statespatent is hereby incorporated by reference into this specification.

Reference may also be had to U.S. Pat. No. 5,909,119 (method andapparatus for providing separate fat and water MRI images in a singleacquisition scan) and U.S. Pat. No. 5,708,359 (interactive, stereoscopicmagnetic resonance imaging system). The U.S. Pat. No. 5,708,359 patentdiscloses further image manipulation, stating that: “Described are apreferred system and method for acquiring magnetic resonance signalswhich can be viewed stereoscopically in real or near-real time. Thepreferred stereoscopic MRI systems are interactive and allow for theadjustment of the acquired images in real time, for example to alter theviewing angle, contrast parameters, field of view, or positionassociated with the image, all advantageously facilitated byvoice-recognition software.” The entire disclosure of this United Statespatent is hereby incorporated by reference into this specification.

Reference also may be had to U.S. Pat. No. 6,175,655 (medical imagingsystem for displaying, manipulating and analyzing three-dimensionalimages). This patent discloses “A method and device for generating,displaying and manipulating three-dimensional images for medicalapplications is provided. The method creates a three-dimensional imagesfrom MRI or other similar medical imaging equipment. The medical imagingsystem allows a user to view the three-dimensional model at arbitraryangles, vary the light or color of different elements, and to removeconfusing elements or to select particular organs for close viewing.Selection or removal of organs is accomplished using fuzzy connectivitymethods to select the organ based on morphological parameters.” Theentire disclosure of this United States patent is hereby incorporated byreference into this specification.

Reference also may be had U.S. Pat. No. 6,486,671 (MRI image qualityimprovement using matrix regularization); U.S. Pat. No. 6,377,835(method for separating arteries and veins in three-dimensional MRangiographic images using correlation analysis); U.S. Pat. No. 5,872,861(digital image processing method for automatic detection of stenoses);U.S. Pat. No. 6,345,112 (method for segmenting medical images anddetecting surface anomalies in anatomical structures); U.S. Pat. No.6,426,994 (Image processing method); and U.S. Pat. No. 6,463,167(Adaptive filtering). The entire disclosure of each of these UnitedStates patents is hereby incorporated by reference into thisspecification.

FIG. 50 shows a cross section of a portion of a medical device 6108around which a magnetic shield 6114 is disposed. The medical device 6108in the embodiment depicted is preferably a catheter with a hollow lumen6110 defined by a wall 6112. In another embodiment (not shown) themedical instrument is a catheter with multiple lumens. In anotherembodiment, not shown, the medical instrument 6108 is a stent withhollow lumen 6110 defined by a wall 6112. In another embodiment, notshown, the medical instrument 6108 is a biopsy needle with hollow lumen6110 defined by a wall 6112.

In the embodiment depicted in FIG. 50, a layer of shielding material6114 is coated onto and is contiguous with the exterior surface/wall6112 of the medical device 6110. In another embodiment, not shown inFIG. 50, the shielding material 6114 is disposed between the source ofelectromagnetic radiation and the wall 6112 but is not necessarilycontiguous therewith. In this latter embodiment, e.g., a layer ofinsulating material, that does not act as a magnetic shield may bedisposed between the wall 6112 and the magnetic shield 6114.

In one embodiment, the magnetic shield 6114 is comprised of from about10 to about 90 weight percent of nanomagnetic material with certainspecified properties. This type of material is disclosed in applicants'U.S. Pat. No. 6,506,972, the entire disclosure of which is herebyincorporated by reference into this specification.

As is disclosed in U.S. Pat. No. 6,506,972, nanomagnetic material ismagnetic material which has an average particle size less than 100nanometers and, preferably, in the range of from about 2 to 50nanometers. Reference may be had, e.g., to U.S. Pat. No. 5,889,091(rotationally free nanomagnetic material); U.S. Pat. Nos. 5,714,136;5,667,924, and the like. The entire disclosure of each of these UnitedStates patents is hereby incorporated by reference into thisspecification.

Referring again to FIG. 50, it is preferred that the shield 6114 providea shielding efficiency of at least about 0.5 and, more preferably, atleast about 0.9. The shielding efficiency referred to is calculated bymeasuring the magnetic field strength outside of the shield 6114 and themagnetic field strength within lumen 6110. The difference in these fieldstrengths is the degree to which the shielding is effective. Thisshielding effectiveness, when divided by the magnetic field strengthoutside of the shield 6114, is the shielding efficiency.

FIG. 51 is a schematic diagram illustrating a typical reaction of ashielded medical device 6108 to MRI radiation. Referring to FIG. 51, andin the embodiment depicted therein, a known radio frequencyelectromagnetic wave 6150 that is transmitted from the MRI unit 6000(see FIG. 49) travels in the direction 6152. As will be apparent, and inthis embodiment, the electromagnetic radiation is in the form of a sinewave 6150.

Sine wave 6150 travels in the direction of arrow 6152 and contactsshield 6114. In the embodiment depicted, sine wave 6150 is at leastsomewhat modified by shield 6114. As used in this specification, theterm modified refers to an electromagnetic wave that is partially ortotally absorbed and/or reflected and/or transmitted and/or phasechanged, and the like.

In the embodiment depicted in FIG. 51, the wave is partially or totallyreflected by shield 6114, to produce reflected wave 6154 traveling inthe direction of arrow 6156.

As will be apparent, a change in direction is only one of the means inwhich incident wave 6150 is affected by shield 6114. As will be apparentfrom FIG. 51, the reflected wave 6154 has a wave shape that differs fromincident wave 6150, and the wavelength of wave 6154 differs from wave6150.

As will be apparent to those skilled in the art, when the MRI assembly6000 detects the shift in wavelength caused to incident wave 6150, itcan utilize its signal analyzing and filtering software (discussedelsewhere in this specification) to identify the reflected wave signaland to also identify the properties of the substrate that caused suchreflected wave signal. As will be apparent, each particular shieldeddevice 6108 will have its own electronic signature and the effect it hasupon a specific MRI incident wave (or waves) can be determined.

One embodiment of the invention is disclosed in FIG. 52. Thus, e.g., andreferring to FIG. 52, a known radio frequency electromagnetic wave 6164transmitted from the MRI unit 6000 of FIG. 49 in the direction 6162 isincident upon the radio frequency electromagnetic wave modifyingmaterial coating 6114 of medical instrument 6108.

The incident electromagnetic wave 6164 is out of phase with thereflected wave 6168, not being coincident in time therewith; see howincident wave 6164 is reflected from the material 6114 as indicated bythe comparative markings labeled “x₀”, “x₁”, “x₂”, “x₃”, and “x₄”. Thereflected wave 6168 is shown traveling in the opposite direction 6166 tothat of the incident wave 6164 direction 6162 only for convenience inillustrating the phase shift which occurs between the incident 6164 andreflected 6168 waves. In general, the reflected wave 6168 direction willnot be exactly opposite to the incident wave 6164 direction 6162.Knowing the reflected wave's characteristics, such as the phase shift ofthe incidence wave 6164 caused by the material coating 6114 allows thesoftware 6018 of FIG. 49 to be modified to either enhance or reduce thevisibility of the medical instrument 6108 in the image displayed to thephysician. In one embodiment, such image filtering is adjusted inreal-time by the physician who may wish to alternately have the medicalinstrument 6108 displayed and not displayed at various stages of amedical procedure.

In another embodiment (not shown) the radio frequency and gradientelectromagnetic waves transmitted by the MRI system 6000 causes thenuclei of the material coating (6114 of FIG. 50) to resonate and toproducing a nuclear resonance response signal detectable by the MRIsystem 6000. Such a nuclear resonance signal from the material 6114 isdistinct from any bio-material naturally occurring in a patient.

FIG. 53 is a schematic cross-sectional view of a portion of a medicaldevice 6200 that comprises a magnetic shield material 6114 disposed ontothe surface of the wall 6112 of the device 6200. The medical device 6200in the embodiment depicted is preferably a catheter with a hollow lumen6110 defined by a wall 6112. A biologically inert coating 6122 isapplied over the magnetic shield material 6114. Biologically inertcoating 6122 may be, e.g., Teflon, Tefzel or other material. In oneembodiment, the biologically inert coating 6122 is an antithrombogeniccoating.

FIG. 54 is a schematic cross-sectional view of a portion of a medicaldevice 6202 comprising a hollow lumen 6110 defined by walls 6112. Thewalls 6112 are preferably coated with a bonding material 6203 before themagnetic shield material 6114 is applied. Applying material 6203enhances the ability of the magnetic shield material 6114 to adhere tothe medical device 6202. Material 6203 may be, e.g., a thin film coatingof aluminum or other deposition of thin film material and depends on thecomposition of the walls 6112 and the shield material 6114. Abiologically inert material 6122 is optionally applied to the magneticshield material 6114.

FIG. 55 shows a cross section of a medical device 6204 comprising ahollow lumen 6110 defined by the walls 6112. The walls 6112 are coatedwith an optional bonding material 6203. Magnetic shield material 6114 isapplied over the bonding material 6203.

In another embodiment (not shown, but refer to FIG. 50) the magneticshield material is applied directly to wall 6112.

Continuing to refer to FIG. 55 and to the embodiment depicted therein, asecond magnetic shield material 6205 is applied over the magnetic shieldmaterial 6114. In one embodiment the magnetic shield material 6205 has adifferent composition than that of magnetic shield material 6114.

Continuing to refer to FIG. 55, an optional outer biologically inertcoating 6122 is applied to magnetic shield material 6205.

FIGS. 56A through 56C illustrate one preferred process of the invention.As is illustrated in FIG. 56A, a biological organism 7002 is shown beingirradiated with electromagnetic radiation 7000 in a magnetic resonance(MR) imaging process. As a result of this irradiation, a signal 7004that represents an undistorted image of the organism 7002 is produced;and, from this signal 7004, a displayed image 7006 is generated. Thisdisplayed image 7006 is representative of the true state of thebiological organism; it contains no significant artifacts.

By comparison, and in the situation depicted in FIG. 56B, the biologicalorganism 7002 contains disposed within it a medical device 7008. In thissituation, when organism 7002 is irradiated with the MR radiation 7000,a different signal 7005 is produced; and an image of this different,distorted signal is presented in display 7006. Due to the interferencecaused by the medical device 7008, the image 7010 is not representativeof the true state of either the biological organism 7002 or of themedical device 7008. It is said that the image 7010 is distorted bysubstantial image artifacts.

FIG. 56C represents the situation that occurs when the implanted medicaldevice 7008 is coated with a nanomagnetic coating of this invention. Inthis case, because the “signature” of the coated medical device differsfrom the “signature” of the uncoated medical device, the image 7012 isless distorted by substantial image artifacts than is the image 7010;and, by proper choice of properties of the nanomagnetic coating, theimage 7012 is representative of the true state of the biologicalorganism 7002 and of the device 7008. The relative accuracy of thisimage 7012 is due to the fact that any interference due to medicaldevice 7008 is mitigated by the presence of coating 7014.

To correct this problem, one may image medical device 7014 by MRradiation 7000 ex vivo, outside of the biological organism 7002. Withdata obtained from such imaging, the MRI may then be calibrated suchthat a correct waveform is generated that compensates for the presenceof the device 7014. This calibration may be conducted in accordance withthe formula D=f [(M)e^(ia)], wherein D is the distortion, f indicatesthe variables that D is a function of, M is the magnitude of theelectromagnetic wave, e is the natural logarithm base, i is the squareroot of −1, and a is a phase factor that is equal to the phase of theelectromagnetic wave that is detected and displayed in the display 7006.

As is disclosed elsewhere in this specification, by the appropriatechoice of materials for the nanomagnetic coating 7012, one may adjustthe phase factor a so that D, as corrected, is equal to 1.

Some of the image artifact problems caused by implanted medical devicesduring MRI imaging are illustrated and discussed in a book by Frank G.Shellock entitled “Magnetic Resonance Procedures: Health Effects andSafety” (CRC Press, LLC, Boca Raton, Fla., 2001).

FIG. 14.4(a) of this Shellock book (at page 281) illustratesintracranial aneurysm clips, some of which contain ferromagneticmaterials and, thus, are contraindicated for patients undergoingconventional MR procedures. FIG. 14.4(b) of the Shellock bookillustrates the image artifacts caused by these aneurysm clips. It wasnoted by the author that “ . . . the smallest artifacts are seen for theaneurysm clips made from titanium alloy and commercially pure titanium.”

Similarly, FIG. 14.14 of the Shellock book (see page 298) illustrates a“T1-weighted, coronal plane image of the hips and pelvis obtained from apatient with a contraceptive diaphragm in place.” The author urged thereaders to “Note the presence of the substantial artifacts and imagedistortion.”

As will be apparent, the process of this invention, when applied tothese and other medical devices, resolves the prior art distortionproblem.

In one embodiment, the radio-frequency wave produced during MRI imagingis a pulsed electromagnetic wave with a pulse duration of from about 1microsecond to about 100 milliseconds. As is disclosed on page 70 of abook by Zhi-Pei Liang et al. entitled “Principels of Magnetic ResonanceImaging (IEEE Press, New York, N.Y., 2000), “RF pulse is a synonym ofthe B₁ field so called because the B₁ field is short-lived andoscillates in the radio-frequency range. Specifically, the B₁ field isnormally turned on for a few microseconds or milliseconds . . . the B₁field is much weaker (e.g., B₁=50 mT . . . ).”

In one embodiment, the pulsed RF electromagnetic wave produced during MRimaging has a repetition rate of from about 10 to about 50,000milliseconds. In one aspect of this embodiment, the amplitude of suchpulsed RF electromagnetic wave is from about 10 microTesla to about 100milliTesla.

The switched gradient magnetic field present during MRI imagingpreferably has a rise time up to its maximum amplitude of from about 0.1to about 2 milliseconds as the field strength rises from 0 to 10milliTesla per meter.

Although the invention has been shown and described with respect to apreferred embodiment thereof, it should be understood by those skilledin the art that various changes and omissions in the form and detailthereof may be made therein without departing from the spirit and scopeof the invention.

1. A magnetic resonance imaging tracking assembly that comprises a medical device having a magnetic shield comprised of a layer of nanomagnetic material, means for contacting said magnetic shield with a first high frequency electromagnetic wave, means for modifying said first high frequency electromagnetic wave with said magnetic shield to produce a second high frequency electromagnetic wave, and means for transmitting said second high frequency electromagnetic wave from said layer of nanomagnetic material, wherein: said medical device is disposed within a biological organism, said nanomagnetic material has an average particle size of less than about 100 nanometers, said layer of nanomagnetic material has a saturation magnetization of from about 200 to about 26,000 Gauss, said layer of nanomagnetic material is disposed between said first high frequency electromagnetic wave and said medical device, said layer of nanomagnetic material has a thickness of less than about 2 microns, said first high frequency electromagnetic wave has a frequency of from at least 21 megahertz to about 128 megahertz.
 2. A magnetic resonance imaging tracking assembly that comprises a medical device having a magnetic shield, means for contacting said magnetic shield with a first electromagnetic wave, means for modifying said first electromagnetic wave with said magnetic shield to produce a second electromagnetic wave, and means for sensing said second electromagnetic wave wherein: said medical device is disposed with a biological organism, said magnetic shield is comprised of a layer of said nanomagnetic material, wherein: said layer of nanomagnetic material is disposed between said first electromagnetic wave and said medical device, said nanomagnetic material has an average particle size of less than about 100 nanometers, and said layer of nanomagnetic material has a saturation magnetization of from about 200 to about 26,000 Gauss and a thickness of less than about 10 microns.
 3. A magnetic resonance imaging tracking assembly as recited in claim 2, wherein said first electromagnetic wave is a pulsed frequency electromagnetic wave.
 4. A magnetic resonance imaging tracking assembly as recited in claim 3, wherein said pulsed frequency electromagnetic wave has a pulse duration of from about 1 microsecond to about 100 milliseconds.
 5. A magnetic resonance imaging tracking assembly as recited in claim 2, wherein said medical device is comprised of a conductor.
 6. A magnetic resonance imaging tracking assembly as recited in claim 5, wherein said conductor is flexible, having a bend radius of less than 2 centimeters.
 7. A magnetic resonance imaging tracking assembly comprising: a medical device having a magnetic shield comprised of nanomagnetic material; means for contacting said magnetic shield with a first electromagnetic wave; means for modifying said first electromagnetic wave to produce a second electromagnetic wave; means for transmitting said second electromagnetic wave from the nanomagnetic material, and means for sensing said second electromagnetic wave; said layer of nanomagnetic material having a saturation magnetization of from about 200 to about 26,000 Gauss; said first electromagnetic wave having a frequency of from at least about 21 megahertz to about 128 megahertz.
 8. A magnetic resonance imaging tracking assembly as recited in claim 7, further comprising means for producing an image from said second electromagnetic wave.
 9. A magnetic resonance imaging tracking assembly as recited in claim 8, wherein said first wave is a pulsed electromagnetic wave.
 10. A magnetic resonance imaging tracking assembly as recited in claim 7, further comprising means for producing said first electromagnetic wave.
 11. A magnetic resonance imaging tracking assembly as recited in claim 7, further comprising means for cooling said medical device. 